I was inspired by this gallery of a French Jacques Schulz porteur bicycle, to copy its rack with some changes to its mounting points. I also connected the swoopy bit at the back, so you could hook a bungee and carry a jacket or sleeping pad. Or maybe a can of coffee.
I think the attachment scheme has some potential, but probably needs refinement. The bottom and seat collar mounting points are slotted, and the collar would mount with the bolt at the front or back, giving a wide range of angle adjustment to mount the rack flat.
