Help needed with (semi) feral play-scratching!!!

Hi everyone. I have a question regarding a semi feral cat that has been with us for a few months. He has made great progress, from refusing to come out when we were in the same room he is now happy to hang out with us, and even follows us around the apartment. I can now scratch his cheeks/chin as well, which I am of course ecstatic about.

BUT - he is very fond of lazily (not aggressively) trying to poke or grab my hands when they are close to him. If I am petting him he will roll over onto his side (showing me his belly), and grab them as if he just wants to lay there and hold them the same way he would hold his toys. Alternatively he will sit in front of me and then stretch until his paws are close enough to my hands to grab them.  His claws are long and sharp (haven't cut them since he is still just beginning to trust us and we're afraid that we might do more harm than good), and it hurts! My hands now look like they have dinosaur scales on them and doing the dishes sucks. 

I have tried everything from saying no and walking away, to to saying no and offering the hand again for him to sniff and praising him when he does, saying no and offering him a toy instead, hissing, sharply exclaiming in pain... I don't know what to do - on the one hand it needs to stop, on the other hand, I feel like he is trying to play and make contact and I don't want to discourage that. I am kind of at my wits end. Anyone have any ideas? 

Its gestures of friendship and love from him...   Although he probably didnt learned himself properly to do it with soft paws.  And him having long uncut sharp nails of course doesnt helps.

Anyway, yes, do mark you are in pain with your voice when he is careless.  This is the way they do learn where the limit is,  being with their friends.

I dont think you shall in any way punish him - as said, it is a friendly gesture.  Quite a few lovinig home cats does it too.

Stefan's right - he's trying to tell you he likes you enough to play.  If he was doing that with his siblings, they'd make sure he knew when he hurt them, so please don't let him get away with it.

A hiss, a sharp "ouch," followed by pulling away is appropriate.  It may take him some time but he will learn when he's stepped over his boundaries.  Redirecting him is also good.

I had to pet on of our fosters wearing leather gloves for a bit.  She just didn't seem to get it and I was tired of scratched up hands.

When grown cats haven't learned manners, it is difficult to teach them.  Please keep at it and don't feel sorry for him!  Just like kids, cats need boundaries and hurting your hands is unacceptable.