J's mom-

Bless you for taking in this little guy in need. I had a litter of ferals a little older than your new kitty, and all but one tamed down to lap cat status. Even the one that never tamed did at least come to trust me and his eventaul new mom.

Two things I did - I did not allow them to hide, and I fed them very tasty treats by hand.

Since he does not have his litter mates to huddle with, he may need a little hiding place to feel secure, but I would make it an "out in the open" place where he is still forced to interact in some way. His crate might be a perfect place, maybe in a quiet corner of the room. But occasionally make him come out and leave the door closed so he can't go in it. Also block any other place he could hide, such as closets and under furniture. This would be a good time to give him his tasty treats, cooked chicken or tuna. It must come from your hand, even if you have to at first just place it in front of him. But he has to associate you with the good stuff, so that's why you want him to see you feeding him. This would also be a good time to bring out good toys, like the feathers, like Spencer mentioned. The feathers would be a very good choice because you can play with him at a distance. But be sure and give him lots of quiet time on his own while he is out, to allow him to get used to his surroundings and let him realize that he is safe.

Since he is completely wild and has probably had no interaction with humans before now (just like the four I had), be prepared for this process to take weeks to accomplish. But like Spencer said, you actually have a very good chance of succeeding.

Good luck, and I hope you find Jasper.