It just so happens that I fixed mine today. I stripped mine a while back when I wanted to look inside the Q4. I was unsuccessful.
I took my dremel and cut a pretty deep clean slot in the top of the head of the bolt. I then inserted the largest flat head screwdriver bit I had in the slot. I then slid a 1/4 inch wrench over the bit and used a large screwdriver to hold the bit down in the slot by prying against it and the top of the exhaust opening. Finally use the 1/4 inch wrench to turn the bolt. I turned the bolt a few times with the closed end of the wrench and then switched over to the open end when it got easier to turn. Oh yea a headlamp really helps you see what you are doing.
My Home Depot does not have a good selection of metric bolts. I wanted a stainless screw because my original was really rusted away on the bottom end of the threads, but they were only available in a philips head for the size I needed which by the way is M5 x .8 x 10. I used a zinc plated screw instead with a lot of anti-seize.