If its not stripped too badly, you could try and put a really small amount of some metal bonding glue, the strong stuff that comes in two different tubes that you mix-forget the name-into the top of the screw(assuming its a philips head) then position the correct driver in and put some pressure on it for a few hours.
It might stick enough to start unthreading it.
Worked for us before at work on a small screw on an Andover BMS/Hvac net controller, it loosened the screw enough to catch it with a small pliers before the glue came unstuck.