>I am currently working on a music video which has the band performing behind a green screen.
Really, the band was behind the green screen?
Try using some sort of edge detection (Sapphire and Tinderbox makes one) on the alpha of the foreground footage, blur this edge and use it as a track matte for a glowed/blurred copy of the background.
You can create a poor man’s edge detector by filling a matte choked copy of the foreground alpha matte with black. Gees, I hope that makes sense to someone else.