In reply to your original post Jen, I use the fairly crude analogy of stopping yourself peeing mid-flow (and I know its a little controversial, but in my experience guys have more success with this analogy than ladies). Can also use the stopping yourself peeing whilst holding in a fart if you're really struggling!! Everyone seems to get it!!
However, I work in outpatient setting, and you may (depending on patient, neural damage to bladder/bowel, control etc) find this an unproductive exercise. But you can judge for yourself.

Hope it helps and that you get some more ideas from somewhere if not!

R.