I'm working on bbg barre chords now and managed to have a couple of aha! moments. With respect to the B string problem, I realized that I had been extending my index finger as far as possible to bar the strings. By extending it more minimally (so the finger tip just lines up with the low E) I found I could get a bit more leverage and even pressure on the strings and it gives my other fingers more room to work with. Of course, after figuring that out I reread Rocky's post and saw that was what he was suggesting as well.
The other idea was a simple suggestion from a friend of mine who is a professional jazz guitar player. He suggested always using a strap (even while sitting) positioned to keep the neck rather high. For me this made a big difference since keeping the neck steady means I don't have to keep adjusting my hand position to a moving fretboard or keep trying to support the neck. Using the strap basically removes the distraction and makes it easier to concentrate on the chord.