I don't know why everyone thinks the backwards one is harder...they are way easier for me. I learned them from squeakers before there was a hang-five. I mean, I just called them rolling squeakers. The only advice I could give you is...speed. I think hang-fives are easier with speed...the same for backwards. When I would do forward ones, carve into a backwards one and then KICK the tire one good time to keep some speed.
Also, this might be in another thread...but since i'm on the subject. Does anyone think that hang-fives are easier with your seat lower? I know the trend today is to run them so high that they are stuck up a birds ass...but seriously, I still think the balance point seems more natural with a lower seat. Anyone care to comment?