Changing Voltage on Non Reference Card

[Tbid]

Hey, I have two non reference cards and I wish to overclock them a bit more but I Can't change the voltage in Afterburner as they're non reference, Is there any way I can do this?

 

[Marine-RX179]

I recall reading that you need Afterburner beta 5 or later for voltage adjustment on GTX570.

 

[Tbid]

Even if the card is non reference?