Thank you for the inspiration. I've recently acquired a side by side with a slightly different intention in mind. Primary fermenting on the fridge side, lagerator on the left. Solves the whole problem of "dedicating the ferm chamber to a lager" for so long. I figure as long as the lager side is cooler than the fermenting side it should work perfectly.
I might try and use some sort of automatic baffle design. Something simple like the one for a laundry vent. Flaps open from airflow, gravity drops 'em when the fan stops.