I've thought about doing the same thing, but I have not yet looked inside the space between the fridge and freezer sections. I have 2 ferm chambers (well, three, but one only works in the winter...) and between them I can control temps on like 7 buckets. So the need hasn't arisen.
My idea was to cut the center out of the space so that the doors could still seal against the front.
Also, it might be useful to replace the door panel with a sheet of smooth plastic. usually you can pull back the sealing strip and unscrew it, take it out and replace it and screw the sealing strip back on.