I destroyed an 8500 using the credit card/screwdriver trick. the GPU is mounted to a pcb which is then mounted to the video card pcb. I broke several of the traces on the pcb that the GPU is mounted to when working/prying up on the credit card surface (or so I thought).
Some people will tell you to put the card in the freezer first and that it comes off real easy, but it depends on how much goo they use from the factory to install the fan unit.
I was sucessfull on my next card, but even then I was real worried as the thing was as hard to remove as the first card I destroyed, but it was worth it, as I easily got another 10-15MHz out of the core with ASII applied. And with ram sinks my card will do just over 300/300 stable after hours of RTCW online
Because the stuff is almost waxy that they use, I would be tempted to try joinT's method. But be sure to keep the credit card squarely butted against the GPU, and watch-out for caps, and capacitors as you pry around the perimeter of the GPU.