I liked Tim's drawing, so I basically did what he suggested:
Truth be told, I hadn't considered the idea of the hinge. But it's really useful for 2 reasons:
1) can easily swing the motor away from the stand and down to lift the bike out when it's time to be a bicycle again.
and, 2) the pivot means I can adjust the pressure against the tire via the bungee cord:
And here's the view of the motor hub contacting the smooth side of the tire: