Toilet training?

We're STILL trying to get Hendrix to poop in the potty. At this point, he's been totally potty trained for like 7 months and doesn't even sleep in a diaper anymore but for some reason, refuses to sit on the toilet to poop. Believe me, we've tried E V E R T H I N G!
The other night he actually did it but our celebrating was short lived because he's even more stubborn now. He said to me, "I don't need to poop in the potty, I already did." So here is a picture of him wearing the little toilet on his head. He was supposed to be sitting on it, "trying" to go but ended up running around like this. Oh well, life is short.