I use a 3/8" bit centered on the allen hex and drill the head of the screw off. This leaves enough of the screw left to get vise grips on it.
Like others have said, all this screw does is keep bolt holes aligned, the rotor is really held by being clamped between hub and wheel. This screw isn't necessary, but it is convenient. On reassembly screw only needs to be finger tight.
Paul Shovestul
QUOTE=angrypancake]So I recently got new rotors and pads for the car, and it's obviously not a very hard job. I got the fronts done no problem, and on my driver's rear side, the rotor mounting screw was stripped to ****, and it sucks because that was the whole reason I was changing the brakes (the mechanic when I first got the car duffed it with rotor replacement ["you need this to pass inspection"] and maladjusted the parking brake and didn't even replace the pads. another rant). Anyways, I tried basically everything in the book to get it out. Drilling it, using a chisel to try and get it, a ton and a half of wd-40 and liquid wrench. Is there anything else I can do?[/QUOTE]
.....Got to keep the loonies on the paath.