3 year old potty training question

Is there someway to be able to train or enable the body/bowel to have a bowel movement at a certain time of day?
The reason I'm asking this is because we've been potty training our 3 year old for the last month and he's doing beautifully during the day with peeing on the toilet. He will stay dry all day even when we go out now. The thing is I haven't been able to get him to have a bowel movement on the toilet! He keeps going in his diaper/pull-up at naptime. We still keep him in a diaper or a pull-up at naptime and bedtime because he's not quite there yet with staying dry while he's sleeping. I know once he gets in the habit of going poop on the toilet that he'll be ok. We've just not been able to get him to go in the toilet!
Also, how long does it usually take for them to stay dry while sleeping at naptime or bedtime? Thanks!

[AHP84]

Oh my gosh!!! Yaaayyy! Finally someone with the same potty training issue I'm having with my son! (Don't get me wrong, I'm not happy for your issue, I'm happy that I finally have met someone with the same problem I'm having).
My son is 100% potty trained during the day (he's almost 3 yrs old), but at night or naptime, he poops in his pull-up while he's either asleep or too groggy to care and get up. This has been driving me *insane,* and all advice I've sought has been useless because no one has or had a kid that poops or pooped in their sleep.
I've *almost* got the problem solved, though. Trevor is pooping in the toilet more than half the time before bed now, but I've been working with him for 3 ½ months. Here's what I've done:
First, I've put extra fiber in his diet during mornings and afternoons. I also feed him lightly in mornings and afternoons. Then I make him a big dinner and hope that he eats more than his fill so that his stomach is so full that he feels like he has to poop within an hour or so (this doesn't work every day, but it works at least 3-4 times a week).
At night, I toss him in a nice, warm, relaxing bath. Then I sit him on the toilet afterwards. Sometimes it works, other times not. It's worked lately, but I actually used to sit with him for, I kid you not, about 45 minutes waiting for him to poop and he wouldn't just because he knew he could go in his diaper.
I finally had it with him one night (last month), and I told him I was angry with him for not even trying to poop on the potty like a big boy. He was shocked! I told him where he wanted to go poop, in his diaper or on the potty like a big boy? He looked me right in the eye and told me his diaper, and to please put it on for him now (he was trying to be polite knowing that I was angry). I said, "Well, sorry then. No mor diapers for bedtime. You're sleeping in underpants."
He had a total meltdown but went to bed in underwear. I did this for a week, and did laundry every day, BUT he learned his sensations and started waking up as soon as he'd mess. He hated waking up in his own messes, so by the end of the week, he started having second thoughts about going potty before bedtime.
Ever since then, he's made an effort to go each night rather than just sit there. I have him back in pull-ups for sleeping, but he usually wakes up dry at least 4 days a week or more.
Also, I try not to bribe my son, but to get him to poop was taking SO LONG, so last week, I caved and told him if he could go poop as fast as he could on the potty, I'd give him a big piece of chocolate (leftover Easter candy). Since last week, I put him on the toilet and he poops in less than two minutes! So I guess sometimes bribes can be justified, huh?
Hope this helps! Good luck!

[April2]

He actually acts like he doesn't want a diaper on at bedtime. He's even gotten up in the middle of the night and took it off and pulled shorts on or something. There's been times I checked on him at 11pm or 12am before I go to bed and he'd be asleep in a pair of shorts and shirt and laying in a pool of wetness. Then I have to get him up and change everything and put him back in a diaper. So I know he's not going to be able to make it all night in underwear.
Naptime thought maybe I can try since it's not so long. The times that I had to keep him up because of appointments or going somewhere, where he wasn't able to take a nap, he wouldn't have a bowel movement! So apparently he will hold it! I know he just needs to get used to going in the toilet.

Also, and this is totally off the subject but he's delayed with his speach. So, if I sat down and talked to him like you did your son, he'd just look at me blankly. He does understand a lot and talks but a lot of it you can't understand. I keep thinking he'll catch up since my first born was a late talker too, but I don't know if I should go ahead and get him into speech therapy.

BTW, AJH84, did you get my email? I wasn't sure I had it right. Thanks for the advice. Maybe this is something that is more common than I thought!

[AHP84]

Got your email, and sent you a looooonnnnggg reply!