USB Extender cable instead
Just get a short USB male-to-female extender cable for each display. Cut a just-big-enough slot in the floor of the instrument compartment, put the female end through, then drill a couple of small holes and use a cable tie to secure the wire to the underside of the panel (pointing aft) out of the way, but accessible. In my single screen system, I fan the extender cable into the glove box, but you don't have that.
For the monthly nav updates - USB update to just one screen will transfer from one screen to the other over the ethernet cable, but the system software updates (about twice a year) have to be done individually from USB to each screen. (Not familiar with the slingshot process.)
Bill H, RV12, N412BR "Sweetie", Skyview-equipped, KASL Marshall TX