Lauren actually sent this to me after a discussion on my struggles in the low range. It's Alan Raph talking about an alternate embouchure for getting really, really low notes. Not quite contrabass trombone low, but close.
I'm always a little wary of shifts and alternate embouchures and other things that could be considered "cheats". I had some trouble back in high school where I had this killer high range, but it came from a pretty major series of shifts that essentially made it impossible for me to play things like the jump from E3 to C#3 in the Guillmant Morceau or a Bb3-Bb4 jump for a solo in Somewhere Over The Rainbow that became a locally famous euphemism for horrific, mortifying failure my junior year.
But that said, I have been trying Mr. Raph's suggestion here, and I've played down to a pedal D. The interesting thing is that working out with this goofy embouchure has actually tightened up some of the regular pedals on a regular embouchure. I can get down to the F fairly well now, if it's still weak. I can't play E or below at all without the shift, and it takes the shift to get any kind of credibility on a G, but that's an improvement over where I was a couple of weeks ago!
Oh yeah, the video: