Hi K.,
Boys can be so smart and so stubborn! My son's the same way. He turned six last December, and even though he does go poop in the toilet, he always has wanted us to wipe him afterward. And we have, with the idea that he would clean himself after he turned six. (This after I saw an episode of Supernanny where she was mortified that the mom was wiping the 6-year-old boy's bottom after he pooped!) Determined not to let this go on any further, we begin insisting that our son wipe himself, with the idea that, once he turned 6, he would be doing it consistently by himself. So, since December, he has pretty much done the wiping himself. Now, he does sometimes call for one of us to come, but we just say "No, honey, this is a skill you need to learn and do for yourself." He would get mad, scream for us to come, but we held strong and eventually he started handling it by himself.
We did do a star chart; if he earned 10 stars for cleaning himself, we would do something fun as a family together, go where ever he wanted. Then we did another round of "star chart"; that time he had to earn 14 stars. He rarely asks for help anymore, and, if he does, I remind him that he can do it. In his case, it was so much about confidence. He didn't think he could do it well, and, frankly, I'm sure he doesn't do a perfect job, but I figure a bath at night fixes that. He's in kindergarten, so I know he has to wipe himself at school (or maybe he just doesn't poop there? I don't know and I try not to worry about it!).
So, good luck and be strong. It's a life skill they just have to learn, but, man, is it difficult to teach. Just know that he will be so proud of himself when he finally makes up his mind to do it.