I've seen a few bikes show up at Free Ride with tags zip-tied onto them that say something to the effect of "this bike has not moved in 30 days and is considered abandoned" (with the Pittsburgh Police logo on the tag).
I assume that the bike at TJ's is on private property, and because of that you would have to call the police to have them tag it. Then they could liberate it after 30 days. At that point, maybe they would let you take it?
Of course, if the bike is a Free Spirit 3-speed, I assume it has one of the older Shimano 3-3-3 rear hubs. Sheldon Brown says those hubs are pretty much garbage. So I would be reluctant to ride on one for more than light duty & recreation.