The hospital i work at is on a university and both seem to create tons of used and vintage bikes that never move.
(i've been thinking about the same thing)

The hospital places notices on all bikes once or twice a year, if you don't move the notice in a week, they cut the lock and donate the bike to a charity (that rebuilds bikes...)
My suggestion is to call the cops, see if there is a charity set up. If not, make one then go cut the cable legally. Or offer you're services as a bike 'towing' company, post a notice giving 30 days, then cut the cable.
Some cities have rules re: parking bikes. If they're parked too long they get towed.
Ask if there are similar in your area, you may be able to take this bike legally.

An interseting observation. The bikes that no-one could liberate, locked with newer faggedabout it chains. They're still there.