Just came across this, and Pearl drums took the words right off of my little typing fingers. The military tried something like that once for Nam. it was short lived. Ninjas had something similar, more like buckets, and poles. The ones the military used had paddles on the under sides, that when you slid the pontoon forward, it folded back against the bottom of the pontoon, and when you slid it back, the blade came down, and propelled you forward. The straps like Pearl Drums said, keep your legs from doing the limbo split!
You could even put bar with a hinge in the middle, and you just slide your legs forward and back alternately. You could put a keel at each end, and the middle of each pontoon to help keep from doing the split. Also you could use a pole with styro foam chunks on each end to help with balance, like dipping one end or the other to help you stay vertical. The Squirrel cage sounds interesting, but it would have to be wide, or have out riggers all over each side for stability, and I guess maybe paddles on the outside, look something like a water wheel.
But for what it is worth, I sent a prayer up for you, and I even tried to look as cute as I could.
Doesn't quite look as cute as when I was five. Actually it doesn't look cute at all.
But I think it is the effort that counts.
Good luck and let us know how you did. That way I will also know wether or not to continue with my cute face routine during my prayers. Could be why they haven't been doing too well lately.
Good luck. Have you thought of simply making a pontoon bridge?
I hope all goes well.
Wayne