I had a problem like this one summer... after I had already learned them....
Anyway, I remembered how to do flat 3's, and just made them more and more inverted. SO I went from flat 3, to whackflip, to backflip.
Another way to look at it would be to kinda transition from a lincoln to a backflip. So if I can explain this right, it might help. So you spot some object in front of you the whole way through a lincoln, just like always. Then next time, when setting up for the lincoln, spot the same object, but with your body turned slightly (so your head is turned to spot the object, maybe 45 degrees off from neutral). Keep going this way until your head is turned 90 degrees from neutral. Notice that the rotation your body is doing is a backflip. SO from there, just do the same body rotation, but with your head straight.
I hope that makes sense haha... That's how I learned them in the first place.