Is the black border, surrouding a just white, like the leader? It would be easy to make a inverted track matte that way.
If not, it will take a little work but you will need to isolate the black borders. My recipe for doing that is to invert the border color channel so they are white. Apply Knoll unmult to it(used to be a free download, but not sure where to get it now). Then apply adjust levels, switch to alpha, and tweak to preference.
Apply this over a black solid and you should have your borders.
Cheers.
Bryan