drlukacs, I was going to start searching, as I know I've seen the instructions out here, but if you have a link or have some hints, I'd appreciate them. I have Gigabyte GV-R797OC-3GD. Thanks.
The first step is getting atiflash (4.07 or later, I would recommend), and saving an original copy of your BIOS. Here is a link to what needs to be changed:
http://www.overclock.net/t/1196856/official-amd-radeon-hd-7950-7970-7990-owners-thread/4200#post_16495299In the case of Gigabyte, the voltage appears at various places, not just as described in this post.
If you have a specific request, I may be able to help.