I think you know what must be done, but don't want to admit it. You need to find a way to get above to hold the nut so it doesn't spin.
Here are a couple more options though. Neither of which are very good. If it is a stripped but or bolt, sometimes you can get enough of a bite on the threads if you can somehow pry sown on the bolt (instead of pushing up). If the bolt hasn't already started to loosen, there is probably no eay to do this. The other is to cust the head of the bolt off and deal with it when you get the subframe down out of the way. Of course, you will need a new bolt as well as any reapair needed to the nut end.
Any other ideas?
