I play the first position Bb like this:
Barre at the first fret with index finger and bring your middle finger down on top of it for extra clamping power. Do a partial barre with your ring finger on the 3rd and 4th strings, 3rd fret (Bb and F notes respectively) then fret the 2nd string, 3rd fret (D note) with your pinky, being sure to arch it enough to let the F on the 1st string sound cleanly. This sounds kind of awkward and it takes a bit of practise to make a quick transition but it works for me and it is highly movable.
Molly, some film footage does exist of Django. I saw a clip of it on a TV concert by Stefan Grappelli. He was on a train dressed as a brakemen or a conductor (I forget which and I'm not confusing this with a Jimmie Rodgers short) and he was ripping off some lightning single string runs. Wether and where it's avalilable I can't say but you might inquire at Stefan Grossman's website or on the Mudcat, for that matter.