While this works it is very difficult to not ruin the material around the bolt.
What I do is use a torx bit. size one up that is slightly larger then the hole and then firmly tap it in. atttach your drive handle a turn slowly while pushing down. this will normally break it free.
Also before your get to this point try putting your allen key in the hole and smack it with a hammer. sometimes the force of the hit will cause the metal to "break" enough that the allen screw wont strip.