Too bad I don't live close to you...I would do it for you for free!! I used to do vet tech, and worked at a Cat-only hospital, so I've gotten my fair share of feral cats.

As for your couch situation - I would get rid of the couch (sell it of course), and use the money for a vet tech to come over and clip nails.

If you have an established relationship at the vet hospital, you can ask one of the vet techs that you feel comfortable with and see if she will be willing to come to your house and have a little extra money on the side. Make her cookies, bake a pie, a small candle, etc as well. Explain the situation to your vet that it's more hassle than it's worth just to clip the nails.

Lastly, if you are able to get the nails clipped after all of this happens, of course it'll grow back quickly, so what should you do in the meantime - put foil on the couch. Cats HATE the foil, and will not jump on there. It scares them (the noise). No mess.

Second to last - if this cat is very skittish, you can give it some calming stuff. Feliway diffuser is good, effective, so is catnip. :-)

best of luck!