Hehe, it came to me in a flash of genius.
Tube, I used a ball on each side (fnar) and joined them by wooden rods (sort of like a nose cone of a plane) then linked them...
bleugh too hard to explain.
Here - I did it again - http://FantasticContraption.com/?designId=1572895
EDIT: The last free level sucks, it's too easy.