Mine is nibbly like that too. You have to establish a difference between nibbling and biting. I'm still working on it, but right now I say "be gentle" when he's biting too hard, if he keeps going, I say it again then put him on the floor for a couple minutes. He's starting to catch on and he's pretty gentle most of the time.
Since Crowley is starting to bond with you, putting him on the floor and ignoring him should be a good punishment because he wants your attention all the time. I just realized, I don't know if he's clipped or not and that might not work

Yoshi is clipped so when he's on the floor and can't get to me he changes his attitude real quick.
That's more of future reference since you can't get him to step up yet. I think for the first week, just spend time with him so he bonds more. Usually when Yoshi starts biting too hard he's already on my hand so it's easy to set him down. If Crowley isn't on your hand already, don't grab him and put him on the floor because you might just scare him and it'll do more harm than good.