The cable connecting the two halves of my ZSA is just a standard 3.5mm TRRS audio cable. Moonlander docs say max length is 6ft~=2m. That should be plenty to route it around the back of your chair.
sure, that's not the issue. The issue is that these mounts let you put a moonlander on tripod bolts. They do not address attaching the so-equipped keyboard halves to the arms of a chair.