I've done that before, it's pretty tricky though, and it's not terribly useful unless they're at low percentage (which could possibly make for a low percent KO) or your first bair is off target a bit.
While we're on the subject of cool 'off the edge' techniques, I've been toying with the instant fortresshog.
Essentially, it's a way to fortresshog on stages that aren't curved instantly.
If you've seen the fortresshogging video, you know that you can do an instant fortresshog from the edge if you're teetering or your back foot is off the stage. So, using the fact that if you're right on the edge you can do instant fortresshogging, I decided to incorporate movement.
It's pretty simple: just run at the edge and use fortress RIGHT AT THE EDGE. If you do it right it'll allow you to fortresshog on any level, regardless of slope, without stopping movement. The timing is really strict though; start too soon and you throw yourself off the edge; start too late and you'll have run off the edge, and you'll still die.
Even still, it's a pretty cool technique to me as far as edgehogging goes, and I've been practicing it a lot to be able to hog on levels that don't have sloped edges, like FD and Battlefield.