L-shaped dining room turned into bedroom

Might be a custom solution type of thing - use the living room PTAC housing and exterior access for the refrigeration components (compressor and evaporator) and then install two split-system-style fan units (evaporators) one in the bedroom and one in the living room. Refrigerant and condensate piping would run from the living to bedroom to support the fan unit there. You could hide those in the walls as you renovate.

A neighbor of mine put a vent in the wall to provide the air flow. I believe he also installed a small fan to push the air through.

Depending on the co-op, you may not be permitted to reconfigure the PTAC, or it may not be able to be rejiggered. You would be better served by finding a real two bedroom. See the "the hunt for a 2 bed apt continues" thread for more on the discussion about the feasability of chopping up living rooms: http://streeteasy.com/talk/discussion/40097-the-hunt-for-a-2-bed-apt-continues

The vent was installed because the owner wanted to move the combined heating/a/c unit or install a second one. This was a condo and the Board voted this down because they had just restored the façade after they had numerous leaks. They also had a number of problems with leaking units that had been addressed. There was also a potential noise problem to neighboring units.