Similarly, for eyes you could have transparent sections that admit light into the interior. Once there various fibre-optic-like bits could direct it towards the central nervous system (or what passes for one in a Flatlander).

Implications of this (using the exoskeleton for seeing) is that soldiers and the lower orders have trouble seeing what's directly in front of them (assuming a mouth at the apex instead of an eye). I can see advantages (in battle, officers have a better view than their men) but you might not like the implications.

You could use the same mechanism I used for excrement for eating, if it's in reverse. It means thaat eating takes longer and is a vulerable time, but that has interesting role-playing implications.