Get him in cloth underpants. You've got the easy part done for you, he'll poop in the toilet, YAY. Now, cloth underwear (either the thick training pants, only needed those for a little while, and/or cool fun undies - if he likes scooby doo, tell him scooby doesn't like to be wet! and if he wets, then plain ol training pants - I really don't see much of them around anymore??!?)
My friend taught me the "2 weeks and $60" method Basically what it was she had her kids running around in long shirts, naked underneath and of course there were accidents, then the $60(or whatever amount it was) was for the carpet cleaning at the end of that period! I think cloth underpants are fine, because they FEEL wet and icky.