Skyjacking takes a lot of things: skill, luck, balls, and more luck. Here's how to do it, thanks to my lucky ass and one dumb pilot who should have known that I would be flying through the air.
Step #1. Launch off man cannon. Notice a Banshee is flying toward your landing spot. Begin hoping by crossing fingers and toes.
Step #2. Hope and pray some more, this time by saying, "oh please oh please oh please oh please." Send off a few warning shots at your target just for the fun of it.
Step #3. Frantically press the RB button, while almost exploding with joy! (A few "OH PLEASE OH PLEASE"s works here too.)
Step #4. Freakishly meld your body into the side of the Banshee, using Halo 3's awesome animation system.
Step #5. Commence ownage.
Step #6. Let skyjackee fall gently to Earth. Laugh.
Step #7. Do a loop-da-loop. Begin Killing Frenzy.
And what does it look like on your screen?
Yes, I did skyjack HalfToed[1]. And it was fun.
UPDATE: now with link to requested fileshare