Princess Auto has a minature impact driver for $10. It was on sale a few weeks ago for $5. Works great for screws like this. Uses standard 1/4 inch screwdriver bits. Much smaller than the usual impact drivers.
I had one Locktited scope mount screw that I couldn't get out. Heated it, broke a bit on it, nothing worked. A tap with a hammer on the impact driver and out it came.
If you need to drill, allen head screws are easy, a ready made pilot hole.
Take a drill bit about the same size as the shaft of the screw. Use a grinding bit in a Dremel or a grinder and grind the end of the drill flat (or use a broken one). Then grind a left hand edge on the drill bit. Use a good drill bit to compare as you work - it's not too hard to do. It doesn't have to be perfect, you're only drilling about an 1/8 of an inch. Don't get it too hot or you'll loose the heat treating.
The flutes are wrong but they only carry the swarf away from the hole - who cares for the tiny hole you are drilling.
Chuck it in a drill in reverse and go at it. You'll probably find that the screw will wind out while you're drilling - the heat and the torque work well.
I've done this before and it's always worked for me.