Thread the bolt in the nut then tap the bolt with a tack hammer to drive out the nut.

Here are a couple possibilities. If you can get to them from behind, try a small pair of pliers, vise grips, or anything else to get a bite on them. I've also been able to get them to bite by using something to pry the bolt up a little while Iturned it. If all else fails, cut the head off the bolt and push them through the firewall. A dremel with a cutoff disk would make short work of this.

Pull and turn. Might have to use some needle nose pliers. It will take awhile. You will eventually have to reach in there to replace it.
Edwin

Do it as Huck says or just take a piece of dowl and knock them out. Buy good blind nuts from your hobby shop, DuBro and install them. Those wonderful blind nuts you buy at the hardware store are made in China and very soft. The prongs tend to bend and break so they don't seat or they come loose. DuBro, made in the U.S.A.!!

You also can use the same holes. What I have done is just atach 4 squares of appropriate thickness new need over the hole on the back side and start over. (assuming your bolt is long enough). If not... get longer botls.. easier than rotating the mount, redrilling, etc.

That's what I do. It doesn't take much of a tap and they come right out.


Pete

I interpretted the OPs msg differently. I thought he ment the nut had broken loose from the wood and was spinning freely as he turned the screw.
Edwin