Intercooler pipe captive nut/bolt woes.

[smudge.g]

I recently decided to fit the viton intercooler pipe o-rings onto my CDTi, that have been sat in the packet for at least 2 years! But before trying, I though i would have a look at the pipe that is fitted to my spare rad/intercooler that came off the scrapper last year.
Upon trying to remove the small nut from the captive bolt that holds the pipe onto the intercooler, the stupid thing just spins in its plastic housing, as the whole thing is a little rusty and there is no room to hold the bolt from the other side! Is there a non-destructive way to remove this nut, thus allowing the pipe to be lifted and o-rings to be exposed??? thanks for reading.