Not true at all. I'm using two 1gb cards, both unlocked. The easiest thing to do is to save the bios from the card, put it in RBE, tick the box to unlock the shaders, save the new bios and flash it.
http://gpuz.techpowerup.com/11/05/29/7vb.png
After you booted up with new bios did you need to reinstall your drivers ?
EDIT:
It seems that my card has modified voltage by default, its showin 1.175 under load on default bios instead of 1.1 so i think i dont need to raise my TDP for the card to work properly
I'll be flashing again and reinstalling drivers after i get back home and ill post up the results, wish me luck so i succeed with flashing