We are also looking into some type of a non-reversible transmission with the clutch.
Ri3D used a Modulox gear box and a mechanical clutch unit to accomplish this and it can be seen in this youtube video at about 1:30. Definitely worth a look.
http://www.youtube.com/watch?v=SWO9OE8JZZk
I would like to help in any way I can but my team is a bit stumped with this system.