Rotobrush Span Question

I have about a 60 frame span:

My technique for using the Rotobrush is go through with the regular brush first, frame by frame, then I go back to the beginning and add the refine brush. It would be great if I could add additional span points, or reverse the span's propegation direction.

For example, I'd like it to propegate backwards from the last frame now that I have added all my brushes. Is that possible?