You are drilling the bolt. Take a 21/64" bit, center it on the bolt (easy to do since the bolts already have a centering point), and drill into the bolt until the hole you are drilling is just past the base of the head of the bolt. Then hit it with the 10mm allen drive and it will come right out. Obviously the bolt will ruined, but they're cheap.
Alternatively, you can use a dremel to cut slots into the base of the bolt. You're trying to relieve the pressure on the base of the bolt head here, that is what's making them so difficult to remove. I'd go the drill route first though, as the dremel option can potentially damage the gears if you slip or cut too deep.