Flashing the bios doesn't do anything for the voltage if there is no voltage control, if you can change the value in the bios the actual voltage doesn't usually change.
For the cards without voltage control it is down to (possible) pencil modding or soldering to increase the voltage.
If you make a thread in the volt mod section here: http://www.overclock.net/graphics-cards-volt-mods/
There are a few people who can help out. To get started at the very least you would need some pictures of the back of the card so the IC numbers can be read, & a multimeter.
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