ORIGINAL: avg_joe
Instead of a dremel, why couldn't you use a drill?
Use a bit slightly larger than the shaft of the screw and drill into the middle of the head until the head is gone. Then when you get the engine out, there will be a bit of the screw sticking out...grab it with a vise grips, and twist.
I really doubt that would work. And if it did, you'd have crap still stuck in the screw hole and wouldn't be able to put another screw in there.
I've done that a few times to my bottom engine mount screws as well. A few times, my dad was able to get them out by pushing verrry hard against the screw and turning the screwdriver. Other times, I just tried over and over, different screwdrivers, and just patience. I don't have a dremel either, but have been able to get them all out.
One time... I actually overscrewed the screw in. I was using a small Craftsman cordless screwdriver to screw one back in (mistake) and it just kept going until it broke the head right off. Luckily I was able to get the rest of the screw out of the mount with pliers.