Repeat the process over and over, retreating everytime he gets nervous. Walk to his side and mess with the stirups, then retreat if he is nervous. Keep doing that untill he is comfortable you aren't doing anything evil. Then (assuming you have a mounting block) place the mounting block next to him, then take it away, and repeat untill he doesn't care. Next climb the mounting block, then get off (repeat) Put a foot in the stirrup (no weight) and then take it out (repeat). Next steps (retreat and repeat after each step untill he is comfortable) lean a bit of weight in the stirrup, next lean on the saddle, next slowly swing your leg over, next you are on!
He doesn't sound unruly, just unsure. By desensitizing him to the process he should relax and be okay with it after a while. If I'm wrong and he's not nervous, just being snotty, then go to mount with him hooked to a lunge line. If he moves, lunge him for a while. Then try again. The point of this is to teach him standing is less work then being forced to run when he moves away