I cannot see the clip here at work (shhhh!) but one trick that might help is to boost the green values a bit on the original footage, and then add the chromakey effect, it might make them a bit more unique. Just don’t do so much that it affects skin color etc.
also check the Vaast site, Douglas Spotted Eagle did a tutorial on using a garbage mask (not that it ever helped me when I used vegas. ;- ) butit might help you.
