Ahh a good ol fashion pencil mod, those things are a bit on the risky side, in case you didn't already know. And good luck on doing it and getting everything to work properly. I doubt you get too much help on Tom's concerning pencil mods here, not too many of us really do those kind of things here it seems I only see something along these lines mentioned once in a blue moon and even than its concerning CPU's generally.
You can edit the cards BIOS to get a minor voltage bump.
I believe the most you can get from it is 1.158v but it is still better than nothing.
Use GPU-Z to pull out the current BIOS, RBE to edit and ATI Flash to flash the new BIOS.
This combo will also allow you to make your overclock permanent and lower your 2d clock speeds + voltage for better power savings.