Thanks, Marie, your post breaking down the steps you used and the video you linked were very helpful! You did such an excellent job with Ollie; it's a very impressive trick to watch!
I'm going to have to work on touching my GCC first. He will step-up 100% of the time, that's no problem. He loves head scratches and he loves it when you wrap your hand around his body so he can snuggle and nap---if he's in the right mood. If he's not in the right mood then he doesn't want to be touched, and if you try to touch his head or body he will push your hand away with his closed beak ("No, thank you, not right now."). If you persist he will try pushing your hand away a few more times after which he will start to nip ("I said no!"), and if you keep trying to touch him when he's nipping he will deliver a good bite after a few nips ("NO!").
I'm trying to reward him using positive reinforcement for tolerating touching at all times but I'm kind of having trouble with it because if I put him on his training perch and I hold my hand anywhere near him---even a foot away---and he doesn't want to be touched he will actually walk over to my hand and push it away with his beak, and if I keep trying he will eventually nip and then later bite.
I'm finding it kind of impossible because I know every time I end up giving up due to the beak push I've completely reinforced that behavior. At this point it's a learned behavior so I have that going against me. However, I have no opportunity to click and reward before he starts to walk over to me because as soon as he catches on that I'm trying to hold my hand near him (usually this only takes one or two tries) he starts walking over the instant he sees it, and becomes increasingly agitated the longer I try to introduce my hand.