4.5 year old intentionally soiling

Hi Everyone, I have been reading through posts on MedHelp for months, trying to find a solution to a problem that consumed our family for almost a year now. I think I have found the solution and so I wanted to share it, in case anyone is feeling as desperate and emotionally drained as I was.
My son was potty trained (pee and poop) by about 2.5 years old. He had an occasional accident, but they were just that--accidents, rare instances in which he did not make it to the bathroom. At about 3.5 years old, my son's dayhome (4-5 kids max) closed and we enroled him in a daycare...more or less a preschool...with 20+ kids total. I think it overwhelmed him. For the first month or two he had an accident every day at daycare (but not at home) but finally became comfortable and regained bladder control for about two months when a scary thing happened to him...he overflowed the toilet at daycare. I can't be sure what was said to him, but he was clearly devastated after that. He hugged into my leg when I would drop him off for the day and started coming home everyday smelling like urine and feces. It was horrible. We would come home with two changes of soiled clothes in a plastic bag. They daycare workers looked at us like we were doing something wrong. We told our son he had to use the potty, tried retraining him with rewards/stickers/small toys/whatever. For a while it seemed to work but then he would regress. His sister (he was previosly the only child), was born about 4 months after he started to regess so I'm not sure she caused any further regression, but I'm sure it didn't help.
Anyway, for about a year now, off and on, we have suffered through encopresis (fecal soiling) and enuresis (wetting, daytime and nighttime). As I said, I was ready to lose my mind, especially with kindergrten starting in the fall. So as a last ditch effort, my husband and I decided to try something "new." I am posting our method here because I am sure others are dealing with this and although kids are all different, maybe it's worth a try, right?
I should first say that some encopresis is due to medical causes....namely, constipation. We had this ruled out by the docs and so we knew that there was intentional soiling going on. Many forums have had posts to the contrary, that kids don't do this intentionally. I know my son was doing it intentionally. The day before this "new" regimen, we asked him after breakfast if he needed to poop (we asked after every meal, as per pediatrician's instructions). He said "no I don't have to" and then proceeded to walk over to the couch, squat down, and poop into his underwear.
So, this one day we decided that we weren't going to help clean up messes any more, nor were we going to prompt him. Prior to that we had given him the responsibility of cleaning his own underwear, which he hated, but continued to poop in them despite this. We decided that he would go back to pullups until HE fixed this problem. He was given two pullups per day...one in the morning and one before bed. If he soiled it, he had to wait until the next time to get a new one, meaning he'd have to stay in it all day. I know this sounds cruel, but we felt that it would show him that he needs to take ownership over this or face the consequences. We also decided that we would highlight the things he lost out on by being dirty and the things he gained by being clean.
First day: We explained these new rules to our son but as we expected, he pooped in his pullup within the first hour or so. That day, we went about our day as usual, going for walks, going for drives, etc. but he wasn't allowed to do some usual key activities (e.g. playground, water park, sitting on daddy's shoulders) because he was dirty. And he had to stay dirty all day. That night he was showered and got to have a clean pullup. My son normally poops 2-4 times a day (when prompted) which I know is a lot, but this day we didn't prompt him at all and so he held it all day. I guess his body couldn't hold it any longer because during the night while he was asleep, he soiled himself.
Second day: He woke up quite upset about this and by now his bum was getting sore and red. We explained to him that this happened because he tried to trick his bum all day and then his bum tricked him by sneaking out the poop at night. He didn't like being tricked by his bum. That morning he was showered and received a new pullup. By now he still hadn't had a complete bowel movement on the toilet in over a day, but we still weren't prompting him. We told him that he could go to the playground and go to the water park and watch a movie before bed if he stayed clean all day. We also told him that he could have underwear back after two days of being clean. After breakfast, he still hadn't pooped on the toilet and sure enough, he got a large smear in his new pullup. We told him that the playground, water park, and movie were off. He threw a fit...the biggest tantrum I've ever seen. he stomped on the floor, yelled, raged. We remained calm and told him he could do that if he wanted but would have to do it in his room. He was ever more enraged. Finally after about 20 minutes, he calmed down and we talked about what had happened and why it was important to go on his own. Then I played a memory game with him and about 10 minutes later, unprompted, "mom I have to go poop I'll be right back." We were so proud of him and wanted to reinforce this good behavior that we told him he could get another shower, a new pullup and have one more chance at the playground, water park, and movie night. He was a new boy after that. He stayed completely clean all day!! We bought a new pack of big boy underwear too and hung them on his door as a reminder of what he could get if he stayed clean. That night there were no accidents, other than normal bedtime wetting, which we don't fault him for and feel he'll figure out eventually.
Third Day: No accidents! Pullup was completely clean! This day's rewards were water park and Toys Story 3 on the PS3 with Dad. We plan to wean the rewards very slowly. He went most times unprompted. I think he feels like he's in control now. We told him that he earned his underwear back for the next day. he said he hates pullups and is glad to get underwear again...keeps talking about it.
This may seem like a small win, but this is a 180 degree turnaround for our son. I will continue to update this blog, especially if there are any set backs. Right now, it looks like things are turning around for him, for the better, finally! :o)