Valve Cover Bolt fails to bottom out....

Yesterday after replacing New Valve Covers - New Gaskets one of the rear bolts only goes into the hole about 1/2 way to 3/4 of the way in before getting tight. I don't want to break it off inside so I have stopped trying to tighten down. I have 2 choices one is to go to the hardware get a shorter bolt - put a stud in with lock tight and run a nut on it. It's the rear bolt on the drivers side under the Master cylinder so I am sure ii would be kinda hard to clean it out with re threading it. What would you guys tell me to do....
I can put a pick done inside of the hole and there is nothing inside of the hole.


Thanks