Heli-coil makes a thread insert for that application but I recommend using a product called Time-Serts. I have used both and the Time-Sert is the hands down way to do it. The only problem is that it will run you in excess of $100.00 just for the kit. I recommend you either contract with a shop to do it or, even better yet, find someone that specializes in removing broken drills and taps. I have no doubt that most cities of decent size will have one of these guys in business. I know of only one in my area, he has been there forever and everyone uses him. If I were to look around for someone like this I would start with the BtoB yellow pages. The guy that I use can do this kind of repair right on the car. When I do them in my shop it ends up running about $100.00 and I use the same stuff he does.

Your concerns about blowing the plug back out of the head are well founded, I have seen that one happen. You mention a temporary fix, let me tell you when a time sert is installed correctly you will never tell the difference by feel and would be very hard pressed to find the difference visually. They are really good stuff on aluminum fixtures.

Good luck,
Mark