Hello-
There are a couple of things you can give your cat to help with constipation. Canned pumpkin (not pumpkin pie filling) is excellent -just a spoonful mixed into a little canned food makes a huge difference. You can also put a little vaseline (petroleum jelly) on his front foot for him to lick off. If he has hair ball impaction, this may help. Finally, you can try a small amount (1/4 tsp of mineral oil) to see if that helps. I do want to tell you that many times, owners think there is a problem with bowels, and the problem (especially in male cats) is their urinary tract. I would STRONGLY advise having your vet take a quick look at him (see link attached), just to make sure there isn't anything else going on. Male cats can develop blockages that will kill them in a very short time, so treatment is important.
http://cats.suite101.com/article.cfm/constipation_in_cats
Please let me know if I can help further in any way.
Breeder
16 yrs health care mgmt & issues focusing on cats, reproductive issues & multicat environments