I'm not sure how much this will help, but it's what worked for me with the Monster. (For which I still can't thank everyone enough for all the advice!)

I kept him caged and gave him treats until he got brave enough to take them from my hand. And as soon as he was given a clean bill of health, I let Zelda into the same room as the cage and let him watch me pet her and love on her. It was actually about that time he saw me feeding her treats and started rather hesitantly taking them from me so that I didn't have to drop them on the cage floor.

I sat by that cage for hours on end and talked to Mowgli and read to him (Huh... We never did finish reading Faust together). And doing all that let him get used to having me around. Then I started dangling a string into the cage and let him play with that (suggested by CCL!). And soon he started to see that I was loads of fun.

It was about this time that I risked a few fingers to haul him out of the cage and put him in a carrier so that I could put the shelves in his cage, and found that he would let me pet him a little. And so I shut the door and started letting Mowgli right outside the cage door for playtime.

Soon I was letting him run around the room I was keeping the cage in. And he decided when he was ready for the run of the whole apartment by slipping by me one night when I was leaving him in his room for the night.

And that's how the Mowg-monster ended up being my little cuddle-bunny. Don't know if it would work with your friend or not. I didn't force myself on him anymore than I felt he was ready for, but neither did I leave him completely alone when he was all hissy either. It was a case of ummm... I suppose a good term would be "escalating levels of affection." You don't do like the Abominable Snowman in the Bugs Bunny commercials and clutch the little darlings to your bosom and "love him and squeeze him and call him George," but don't go, "Boohoo! He doesn't like me!" every time he hisses either. Don't know if any of that will help your friend. It's just what worked for me.