It would be fairly simple to weld an extension onto a LH drill bit and try backing the stub out that way. The back of a drill bit is tough, not hard, and I've welded plenty of them in the past when I needed a long bit. I can make you a drill guide from oil hardening drill rod that will keep the bit centered in the head bolt hole if you wish.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!