i've only just started backrolls, and before i was trying to initiate the spin before the pop. this resulted in loosing loads of pop and doing a poor roll.
i've found that now i approach the wake as normal, and at the moment of popping, i throw my hips forward and shoulder back. this would be the same if you were doing it off a trampoline, u'd initiate the roll as you jump, not before. This then allows you to use the same pop as before, and then give yourself more air time to spin.