I don't know if you can do this, but on severely mauled exhaust bolt heads I've hammered then welded a grade 8 nut onto the bolt head. This gets the bolt good and hot, too.
I have also welded cheapo box end wrenches onto bolt heads. Once it breaks loose, use the cutoff disc or Mr. sawzall to remove the remains of the wrench.
If you can get the dremel to one side of the nut you could also grind through to the bolt.
Good luck, you will prevail. I think the hardware now knows the Apache tribe is ready to kick ass.
Bulldog aka Ronnie