Re: Knocking off the rust
A good method in my experience is to get people to do a backwards roll from sitting on the mat, and then to play with reversing the backwards roll at various points during it so that you ultimately becomes a forwards roll.
E.g. roll backwards half way and then forwards, repeat a few times. Roll backwards until your feet start to touch the mat, then forwards, repeat a few times. Finally roll backwards fully so that you are upright again (on your knees), and now reverse it into a forwards roll. This shows them how to get the shoulder down on to the mat.
Backwards rolls are very unthreatening!