Oh man, do I feel dumb. Turns out I've been holding down L1 while I glide, thinking that it keeps my wings out. After extending the wings, however, L1 becomes your airbrake. No wonder I was having problems gliding. After learning this, I made it on my first try.
I'm sorry Transformers, I love you.
It's worth noting that I've been stuck at that point since May 9th, 2004.