You can often take a crap screwdriver and wedge it into the now-damaged hex head cavity. A pair of vice grips clamped to the screwdriver give you all the leverage you need.
You may have to file or mod the shape of the screwdriver head a bit.
This is Africa, 1943. War spits out its violence overhead and the sandy graveyard swallows it up. Her name is King Nine, B-25, medium bomber, Twelfth Air Force. On a hot, still morning she took off from Tunisia to bomb the southern tip of Italy. An errant piece of flak tore a hole in a wing tank and, like a wounded bird, this is where she landed, not to return on this day, or any other day.