Thats awesome that they will lend you the weights. But just for the sake of giving you ideas...
You live in an apartment?
Make a sandbag. Or put heavy stuff in an old bookbag. Or be really crazy and do both. (Ex. while squatting you can wear the backpack and hold the bag, etc)
Be creative, its a heavy awkward thing. (Overhead press, squat/deadlift, pushups with it on your back...)
Whatever movement you are doing, use the bags to make it harder.
Pick it up over one shoulder and walk up stairs and back down, drop the bag, shoulder it on the other shoulder, and do it again. Become tired.
Its not ideal, but its crazy versatile, and a lot better than nothing.