Originally Posted by Heidi:
Put it on HIM, not you.
"my darling son, you are simply TOO OLD to be wearing baby diapers. From now on, I expect you to use the toilet like a big boy. So, if you have an accident, you will change yourself. I will NOT do it for you.
Then, keep your cool, and help MINIMALLY just to keep any major messes at bay.
Put a pile of clean clothes and undies in the bathroom, a hamper for soiled clothes, and a pile of wet wipes. Put paper towels and soap-and-water in a sprayer nearby, get rid of your bath mats for a little while.
If you see he's wet, simply say, very matter-of-factly "Son, you are wet. We do not play in wet clothes. Go change please, and I will guard your tower/lego building/ball for you while you're gone. Let me know if you need any help, please". Put up his toy, and wait. IF he calls for help, then go help him MINIMALLY. Just enough so that you don't end up with 85 dirty paper towels and a wall full of poop or something.
Next time, same thing. It's got to be more inconvenient for him to change than to just go.
If you see him doing "the potty dance", say "Oh, I see you're doing the potty dance. Do you want me to safe guard your Legos for you while you go potty?"
You've got yourself in a power struggle you can't really win. Make it his business vs. yours, I say. You're just there to assist when he makes a mistake; it happens. Show him how to fix it. 
Thank you!! He does change himself now with his pull ups but I think switching to just underwear could help. At this point, it can't hurt! Lol.