I am probably the worst person to be giving advice on this, but I have had Rene for 1 week now and have endured few bites already, I had to sit there the other night after a good bite on my finger, bleeding (I was actually dripping!) Asking Rene "why are you biting me?" my boyfriend James was looking at me in horror I think he was thinking that I was going to throw the bird, but even as he was clamped to my finger I explained to James and Rene that he WILL NOT win, and lunging is NOT an acceptable behavior.. Balling my hand into a fist doesn't work for me either, Rene still can grab at my skin, or he has learned to go for the edge of my hand.
But good news is, I have learned that once I get Rene onto my hands talk him through his pinning eyes I can ask him to step up over and over putting a new hand out each time, and then put him back to his cage, and right away ask for a step up and not get bitten.
Also if you just stick your hand in right to the bird and ask for a step up DO NOT HESITATE seems to work best for Rene, if I go to slow or am not perfectly clear on what I am asking it always leads to a bite.
I just wanted to add that this is what I do on the advice of the previous owner of Rene who had him since he was 2 weeks old and knows him will enough to know he will benefit from me being pushy, I don't think that I would try it this way with any other grey I would be in the same position, asking the wonderful minds here for advice!!