Hmm, this would allow me to mount my PBSF clone where the 4D is now, put the 4D back on it's seat post adapter, and the Cherrybomb can go above the 4D...

And why would I want to do this, you ask? Simple. The strength of the 4D is the side visibility, but when I use my Townies, I have to mount the bags as far back as possible to avoid heel strike. Which blocks the side firing LEDs of the 4D.