Feral kittens can almost always be tamed, but an adult is a real crap shoot. What can be very successful is preventing the cat from hiding - spend time in the room but don't ever actually approach him. At the same time, block any hiding places or place him in a large crate. Ignore him, and that will make you not seem as threatening. After awhile he will stop being stressed out by your presence (or not!). When you notice he is more relaxed, start approaching him, but make sure that when you do you either have some really smelly, yummy food treats and or an irresistable toy - like the feathers Spencer suggested. When he is relaxed even when you approach him, then start trying to stroke him, being careful always to approach him from underneath or the side - in other words, don't try to pat him on the head at first because he may perceive your hand coming at him as a threat. Try stroking his cheek first or his back, without approaching from above (I hope this is making sense). This could take anywhere from several days to several months, and it still may not work.

But you're right, even if he never becomes a lap kitty, his lot in life has still been vastly improved by your kindness!

Good luck with the little guy!