I'm running 32-bit Windows 7. What you can probably do is to modify your card's BIOS. I've read stories of people flashing their cards' bioses with reference ones from ATI and/or editing existing power states. There are number of tools to do that, for Windows only I presume. Personally I have never done such a thing as my mining rig is a dedicated one and I had access to a genuine Windows 7 license.