124 window regulator bolt is spinning.
 

I am trying to change the window regulator but one of the bolts is just spinning in the rubber mould on the back side of the regulator inside the door. No access to counter hold. Anybody has encountered this before? Any suggestions as to how to remove it? The bolts on the regulator are sitting in a hard rubber/plastic like compound and one of them started to just spin around when I tried to take the nut off. Looking at the new regulator there is where little I can think of how to counter hold the nut while the regulator is still installed in the door. Any help is appreciated, Alex