You could try helicoils. I have used them in heads so they can get hot. An older trick is to cram foil in there and then the threads will catch on the foil and go. You could also get some metric studs that are slightly larger and use them after re-tapping. I have done that as well. JB Weld might work - people have used it on blocks. One other option is to change to a regular bolt - pass it through and then put a nut on the end of it. I have done that as well.