Originally Posted by Freebase Dali

You're doing it wrong.
Coax him out with soft cat food (You know, those cans of chunky, gravy-filled deliciousness) or a bit of tuna.
He will come out. Hesitantly. But his desire to eat the food will overcome his apprehension. When he's eating, you can then begin to pet him gently so that he knows you're not going to hurt him. At first, he will flinch. When he stops flinching, you're good.

When he's done eating, don't make any sudden movements. Just sit there. Let him survey the area on his own terms. He needs to find out if he's in someone else's turf. Don't make him think he is. Let him sniff around and acclimate.
In a couple hours, he should be confident enough to walk around. The first day or so will be all about exploration.
When he's done exploring and assuring himself that there are no dangers lurking, he'll open up.

Just let him do it on his own terms. Don't force him into anything.