My cat has the same. I keep it under control by giving him cisapride three times a day and a treat that I make with Pill Pockets and Miralax (or store brand). Talk to your vet about Cisapride. But the treat arose from the vet's recommendation that I give him a quarter teaspoon of Miralax three times day. It was just easier to buy a bag of Pill Pockets, empty it into a bowl (I use a mortar and pestle with a smooth interior), measure out ten teapoons, knead it all together, mixing it well, rolling into a ball, pressing it out on a counter or some hard, flat surface, shaping it into a square, and cutting into 40 even pieces. Sounds like a lot of work, but the mixture lasts about two weeks at a time. I don't know of any concoction that is out there.
The colon could be enlarged because it's full of feces. That is another cause of an enlarged colon. If the colon enlarges too much, there's a very strong possibility that the colon will rupture and cause a massive infection that will be very hard, if not possible to cure. If the obstruction is not relieved in the next couple of days, then the rupture is a real possibility. First, the cat will stop eating and drinking, then you will see vomiting, and then your cat will develop a very high fever. The high fever will tell you that the colon has ruptured and caused an infection. If you don't believe any of this, do the research and you will find that this info is correct.
This condition has gone too far for you to even attempt to treat this at home. If you want your cat to survive, then you must find a way to get your cat the vet care that a good, caring, RESPONSIBLE owner would do.
Try calling around to different vets' offices and see if they will take post-dated checks, or try care credit-a special credit card for pet care only. They can be found at carecredit.com. Please, do the right thing.
Well, I am not sure if this will work for chronic constipation, but canned pumpkin works very well as stool softener. Yes, you can just go ahead and try it, and since pumpkin is kindda sweet, kitty will most likely eat it.
It is very important that you prevent him from being dehydrated. If necessary, use a syringe or eye dropper; that is, force him to drink water by sticking a syringe in his mouth. The only bad thing about this is that it stresses the cat, but at least he'll be hydrated.
Now, I need you to read this very carefully. If the vet told you that your cat's intestine is enlarged, then your cat is suffering from a condition called Megacolon. You absolutely CANNOT and MUST NOT give your cat enemas. Only the vet can do this. In addition to that, what your vet wants to do is called Colectomy. I've heard many cases of Megacolon, and the prognosis when surgery is performed is favorable. You can choose to do the surgery, or you can chose to switch him to a diet higher in fiber first, and if you see no results then surgery would be your other choice. About the fiber, you may want to switch your cat to a diet that's higher in fiber, or alternatively, adding psyllium, wheat bran, or pumpkin to each meal. Also, I would ask the vet what type of suppositories to get. Your kitty may just feel better with those. That poor thing's inflammation inside may be hurting him a lot.
Let us know what you decide. Good luck to you and your kitty.