I agree with the butter knife trick, i have used it before and it worked,
however i am not to sure about the freezer thing... I have heard about it, but it makes little difference (I think).
Another good idea if you are using the knife trick, is to put a credit card inbetween the GPU and the actual card (if it can fit),
just to make sure when you TURN the knife it does not damage the card...
Imortant though, you DO NOT wedge it off, you turn the butter knife as if it was a screw driver. Clockwise, Anti-clockwise ect.
I have done this before
hope this helps!