The TJ front pipe will bolt up to an aftermarket YJ catback, but it is easy for a shop to bend you a front pipe, and weld in the o2 boss. Make sure it's in front of the oil sump as high up as possible, and they leave room for the starter to be dropped down without removing the exhaust.
Somebody had mentioned using a left-handed drill bit, so it's possible to back the broken stud out if the bit grabs hard. If it doesn't grab hard, it's time for the easy out.
I'm not familiar with using a helicoil, but from what I understand you can drill the entire stud and hole out larger and insert a helicoil for the new stud to grab.