Photoshop :: Rotoscope "fringing"

I've composited 16 rendered frames to simulate movement. I did this by rendering one still of the entire scene, and then rendering 24 frames of the arm and boot ONLY in motion against a green screen. Then I overlayed the whole thing in CS, used the magic wand to select all the green screen in each layer, deleted that, adjusted the layer transparency, and then, when everything was set up, flattened the layers. The problem I ran into was this, a green "fringe" around the arm and boot on each layer that'd been green screened. I wound up having to set the magic wand tolerance to 175 to get the majority of the green, but that also ate some edge detail that I would rather not have lost. Is there a way around this?? It occured to me that maybe rendering an alpha image of each green screened frame to use as a mask might do the trick, but I don't have the software to automate such a process, or the time to do it manually.