Haven't had need to try it yet, but I have thought of a possible way to tow one or two bikes behind another using my Burley Flatbed Trailer.

Put a cross piece on the front and the rear of the bed rails of the trailer.

Attach two cross pieces to these that run the length of the trailer (four for towing two bikes). Space these so that the front wheel(s) of the bike(s) to be towed will fit between them.

Place the front wheel of the bike to be towed on the trailer, between the lengthwise cross pieces and tie the front wheel securely to the trailer.

I have considered if a set up like this would have a tendency to tip over, but with a two wheeled trailer like the Burley I don't think this would be a big problem for a single bike if it were centered on the trailer. If towing two bikes, the back wheels would add to stability. I think. Like I said earlier, I haven't tried this.