I have designed a 2-element elevator card for the tower system. For the class I teach, the full 4 card elevator was a little large for the smart cars.
I just ordered prototypes and should have them next week. If anyone is interested in purchasing a pair let me know.
These should work on the primary and secondary sides. I simply passed all of the I/O between the PCI-E pins. The power pins have wider traces and there is a ground plane poured on the bottom side. There are also LEDs on the +3.3v and +5v lines.
See attached 3d models!