I've been able to get cider with potasium sorbate to ferment out but it didnt taste very good - especially near the end of the ferment. Probably because the yeast were not reproducing and were getting old by the end of the ferment. It might be worthwhile doing a 2nd pitch halfway through.
Next time, see if you can talk the folks in the press into selling you some juice before it hits the UV and they dose it. It will clear better and taste better. Most likely, there is someone at the press who makes hard cider or has friends who do. If you talk to the right person at the press, they can hook you up when it is time to press the good cider apples.