Find a steel bushing/dowel whose outside diameter is the same size as the inside diameter of the threaded hole. Now find a drill bit whose outside diameter is the same as the inside diameter of the bushing/dowel. Drill slowly, using this method will ensure you are drilling the center, go slow and let the bit do the work don't push or the bit will walk.
Also since it's aluminum I have and the bolt in most likely stainless I have welded a stud into the hole onto the top of the broken part and then just unscrewed it......
The key to all of this is absolutely take your time, if you rush you will make it worse and the problem will expand and become more difficult.
Scott