what if an ID was generated and printed just before voting with an option to print an arbitrary number of additional ID's of already voted people. the boss never knows what ID(s) he'd receive.
So you come into work on Monday thinking that everything will be peachy-keen, and get an all-hands email telling you that any employee that can not prove that they voted for the "correct" candidate will forced to resign.
Any system that can be abused, will be.