try some leather insole for the front of shoe ONLy or something similar which i cant remember the name of. its meant to bring your sole UP and therefore prevent it from sliding...
however there is a new prodcut made by SCHOLL calles "PARTY FEET" gel cushions specially for heels.... see if you can find them
yeah, that's what I was going to say. Try things from Dr. Scholl's. People always enjoy his products. I was wondering about those gel inserts myself. You should try them. I also saw this product at Girlshop. They are slip resistant tabs for the inside of your shoes. here are the links