i cant do them myself, but ive been watching a lot of videos because mine look like this and i want them to look like moe gold's
) i think the key is to initiate the roll with ur hips, rather than bending your front leg, so as soon as u've popped you push your front hip down and round to start the rotation, and let your shoulders follow. but im only guessing from watching the wakeboarders do it behind a boat, see if it works!