No easy way out here. I had the same problem. On the way back from Florida to the frozen north (minnesota) my exhaust got louder and louder. I had one of the 5 studs holding the exhaust on and likewise no bracket, presumably removed by previous somebodies, and then there were none. So bailing wire had to do for hundreds of miles.

The problem with trying to drill them out on the car is that even with a close quarter drill / Milwaukee-Sioux it is hard to drill in the center of the broken stud due to not being able to see or hold the drill accurately. I have just relearned these lessons first hand. I have broken exhaust studs in both of my 245ti's. I was able to drill out 3 broken studs and on the 4th one I broke a hardened easyout and now I will probaly have to pull the head.

If you remove the turbo unit you take the manifold off and the turbo comes with it. None of the work is difficult, but it is time consuming. Replace the exhaust manifold studs now as they are sure to break later. The only tricks are getting the turbo oil drain pipe back in with out chewing up the rubber ring that seals it to block. Hang the exhaust manifold on the new studs and from underneath place the tube in its hole in the block, move the manifold closer to head and loosely install the two bolt that attach it to turbo, making sure that the drain pipe is centered and tighten everything up. Oh yes it is best to remove the O2 sensor and install it after manifold is back on head as it is easy to break the wire as it is a bit of a Houdini act getting the manifold/turbo of the space provided.