I just posted to your other thread on this topic.

Basically, you should install the other bolt on the same side of the mount and crank it down tight. That will hold the carrier in place so you can apply some force to the broken bolt.

And, again, I'd go after this with an external-type stud extractor instead of an ezy-out. No drilling required, and it should make the job a breeze if you have a quarter-inch or more of broken stud to work with.