I removed all 12 exhaust-side studs with these gizmos from Sears. The #4 fits over the threaded ends of whole studs and the #2 fits over the unthreaded remains of the broken studs. It worked well even on stubby remains (slightly shorter than shown in the previous post).
If the end is broken at an angle, you may want to square it a bit with a Dremel so the gizmo sits straight. Tap it with a SFH to seat it so it bites into the stud. Use an air wrench instead of a breaker bar (more twisting, less bending).
I removed mine cold, but heat could only help. (I did have two of the longer ones break). The only ones I couldn't remove this way were flush with the case and had to be machined out.
YMMV, good luck.
Steve