can you change gears once you're up? basic physics means that the hardest part of the wheelie is getting the front up the first 45/50 degrees, with different gearing you'ld be able to pop it up and flick through the gears, it'd also help with getting it up from a rolling start in second.
i remember a guy on the old ez-board forum had gone down one tooth on the front and up 3 on the back on his 250 and claimed to be able to do rolling burnouts and wheelies with ease.
If you're doing a lot of stunting it might be worth getting an engine cage fabbed up for yout bike, the engine casings on the bandit grates away like soft cheese in a slide.