A few hours ago, Shamino posted a thread at kingpincooling forum.
ASUS R&D have somehow figured out a way to publish voltage modifications for graphics card; these include control VGA loadline, switching frequency, OverCurrent Protection and core voltage.

Control Load Line, Switching Freq, OCP, Voltage of 7970 with R4E
First solder red and black headers to VGA card:

The headers will be later on plug into MB.

Steps

Do Not plug in the header before boot.
After Boot and go into OS, plug in header
Open Digipower CNTRL (install from CD)

you can set load line, Switching Freq, OCP, it will be set with the CPU’s vcore, so suggest set LL Extreme, Switching Freq 500 to 800, disable OCP (this will also be used for the VGA Vcore)
If you also wanna adjust vcore of VGA, u can open up Turbo V and adjust the CPU Vcore together with the VGA vcore. VGA vcore will be 100mv lesser than what you set on the CPU. For eg, 1.40 will give 1.30 on VGA.
After adjust and ready to bench remove header. Settings hould be kept even at reset unless you shutdown.

Do not have the header plugged in at boot as it will make the system stop booting.
Enjoy.