What things can be done mechanically to make the ISS more stable in a dormant state without a crew?
I have listed a couple of links that may work, but I am open for constructive criticism and new ideas.
Adding a long pole to the station (particularly with sufficient mass on the end) will increase the station's moment of inertia. This will reduce the effect that a perturbation will have on the station's attitude. However, it also makes it more difficult to correct an error in the attitude.
The reaction wheels that are already on the station are a better solution.