You've gotten some of the best advice on PT from people who work with ferals and unsocialized cats all the time.

Our Norbert was like that when we took him in - his former caretaker (using that term loosely) did not EVER pet him - he spent all his time with 4 other cats on a screened porch. When we took him in, we set up a big kennel cage for the first week in my home office - he was free to come and go, but he felt safe in there and stayed there. I fed him, talked to him and worked in there most of the day with him watching me. The other cats came and went and everything was our normal routine. Within 3 days I was petting him and withing 3 months we were able to brush him, sit on the sofa with him and he wasn't hissing at us everytime we came in the room. But if we hadn't set up the interaction, I don't think it would have turned out so well.
Oh, and have yummy food treats with you when you do this. Associating you with something tasty is a good thing!