Some notes on the installation of these
DO NOT GLUE OR MELT THE BUTTON
The covers on the back of the riders come off easily with a small flat blade screwdriver. I have down at least 6 of these bikes without breaking anything. First unscrew the ornament hook holder and then gently pry off the cover. Remove the switch and solder the two wires together.
Also the battery polarity is opposite on the small batteries to what you find on AA and AAA's. The positive is on the spring and the negative is on the flat plate. Cut a little notch in the battery cover to let the wires feed out.
Also I put the screws though the wheels so that I don't need a ton of spacers/washers to hold the bikes in place.

Wish I would have saw this before I did mine- I ended up with one that turned itself off after 5 mins and another that wouldn't come on after gluing. Nevermind though, I split the top off the bikes anyway and hotwired them. SOOOOOOO much better and SOOOOO much cleaner. Only way to do it. Just take your time, especially on the Clu bike. Note, I didn't do anything but snap the cover back on. If it falls off I'll think about gluing. Some pics below.

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A little late -- but I went with an approach that was fully reversible. I just drilled a small pilot hole into the wheel and used the existing screw. For the other wheel I used some of that putty stuff that comes up. Various names for it and I can't remember it offhand.