I put the wheels back on Herc and used that for the test. You may notice in the photos that my test subject lacks a number of parts, including the saddle and brakes. I tucked some pieces of old excercise mat under the naked clamped rim to give it some protection against bumps.
This set-up works fine while walking the lead bike in a straight line. The primary flaw is that I made the end pieces too long, so that if the clamp gets pulled out of position the slightest bit it rubs against the trailer wheels. Some of this problem might be fixed by using a more rigid tie-down technique -- I used bungies because they were quick and would give me an idea. Really I should just saw off the last inch or so at each corner, though.
Also, the clamp wasn't as stable as I'd hoped, mostly because the floor of my trailer isn't actually flat, it's a sheet of plastic that has started to deform wherever the frame doesn't support it. Again, rigid tie-downs; I'm thinking maybe those heavy giant Twist-Ties I saw at Home Depot....
The tow subject (if you will) tended to rock in the clamp -- proper tires would probably have helped -- which allowed the front wheel* to wobble and even flop far enough to drag sideways. I hope solving the above-mentioned issues will fix this enough, but I may have to come up with a way to brace the handlebars/fork to keep the wheel straight.
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* actually the last wheel in the line while towing, but you know what I mean.
