You can get wedges from the hardware store. They are like shims that go under the fronts of bookcases etc, so that they are essentially leaning back. It means that they can't pull them forward with their own weight. Worth a try I would think.

The other thing is to ask the owners permission to bracket the furniture to the walls. Make sure you offer to fill and repaint the holes when you move out. Again, worth a try!

GL