Originally Posted by UniChris

Have you considered a little crude blacksmithing? If you can get some crude indentations in a piece of a drill rod, and then file to fit, harden, and temper you might end up with something decent. We made straight screwdrivers that way in high school shop, and something more complicated should be possible, worst case you do it all with a file or maybe start with a dremel disk. If you don't harden and temper it it might still last to get the originals out, and then maybe you could replace with a standard head fastener. It's also possible something that only hit two of the three wings would work for extraction. Or what about just taking them out with a left hand drill bit and screw extractor set?