haha, sorry that was unclear. WHen you move his butt to the left, you use a bit of right rein, right? So instead of pulling back towards your hip, or out away from his neck,(which will allow his left shoulder to bulge left) lift your hand up. Does that make sense? So instead, pull on the rein like you're lifting a glass to cheer with, straight upwards. It wont have to be very high, depending on your horse. The higher your hand, the more movement you'll get in the back (with leg of course). It might only take you raising it slightly, you'll have to play around. Its just a more clear messege and is leaves no room for anything but the butt to move. That way you don't have to beat around the bush. :)
When he stops, and turns his hind end, I m m e d I a t e l y turn his butt the other direction. So that you are constantly contradicting his decisions. Not only is this a willingness exersize, it also gives your horse a clear, constructive, firm direction that he can follow, and learn to trust you instead of deciding for himself.
I would avoid ( if possible) the whole circles, as it ma give him a gateway to the rear unless you're on top of his steps every second of the way. Keeping his front end pointed in the direction he doesnt want to go is key, like you said. Just move his but from left to right, left to right. Once he takes a step forward, release immediately for a second, then continue on. You want to feel that all of the sudden he wants to take you past the point he was refusing, rather than you making him. If he scurries past, that's ok. Just walk on for a few then turn around and do it all over again.
Say you're trying to move his butt right but he just wont budge. You might carry a stick and pop him on the right side of his hind end until he takes a step, then switch again. Whips come in handy.
I hope that clears some things up. You def. Have the right idea. Its that he's being a little naughty, yes, but prob. Insecure. So if you handle this with the approriate intensities or softness, he'll resort to just moving forward.
Good luck! (remember to always be looking up and ahead of you, so if he pulls any spontaneous acrobatics you're ready!)