Swolf, if i have to remove a broken stud, the last resort is an easy out, with the expectation that it will probably break. I have used various designs similar to easy outs, with various success.
I haven't used the fluted EZ outs, but they get good reviews, depending on brand. Some are soft.
I wouldn't use the hollow cutters as I expect they would wander off and damage the cases.
An interference fit bolt is always going to be difficult to get out.
Another method that has a good chance is welding a nut onto the broken bolt shaft, if there is enough sticking out to get onto.
The best option is the have a beer and hope it jumps out itself.
Cheers