Thanks to Q's welder, the bike mobile is complete. I designed and made the front wheel holders, so that four bikes and wheels can all easily mount to the front of the trailer.
This picture shows the wheel mounting brackets protruding from the wooden structure. Clicking on the photo enlarges it. Details are then easier to see.
An action photo of me welding the mounts. (I pulled this image off of Q's "queasyfish" blog.)