I came up with this contraption for days when my kid needs a pick-up from school. He rides the bus to school, but on days when he has sport practice he misses the bus home.
I was inspired by this blog post which describes the idea of strapping the front wheel of one bike to the back of another. But my version uses a board with strap mount points that attaches to three MIK Side studs on the side of my rack using 3D-printed sockets.

The secret (that I learned from that blog post) is to make a tight strap connection from the head tube of the towed bike to the rack of the tow-er so that the towed bike doesn't fall over sideways.

It seems pretty secure. But my bike wobbles continuously while towing. Not too badly, but enough to discourage me from making hand signals. I think maybe because the rear wheel of the towed bike is not in line with the wheels of the towing bike. Or maybe because the steerer tube of the towed bike is leaning a little to the right.

I'm thinking of trying another idea I read that would line up all the wheels: attach a spare hub to my rack, remove the front wheel of the towed bike, and use the axle to connect to the attached hub.
when he was younger and it could be wobbly even though it was perfectly aligned. At least when he wasn’t paying attention to his balance too!