i'm assuming you mean in slam dunk contest- and the answer is, simply, do the slam dunk tutorial. it will show you. but i'll tell you, if you don't have the patience for the tutorial, just to mess around with pressing (and holding) L and R, and then the way you toss the ball is with the yellow "c-stick". try pushing it different directions, spinning it in a circle, etc. it takes ALOT of practice. L and R are your "modifiers" that help make it different.
hope that helped, but i really do reccomend the slam dunk school thing.
and if you mean in regular game play (not in slam dunk contest), you're out of luck. you can only do that kind of stuff in slam dunk contest.
