...and the one on the far side is one of those handicapped jobs.

At this point a judgement call is in order.... Are there any "insert PC term here-challenged" people working here?

No - It's fair game (and the one thats always occupied.)

Yes - see if there are any devices that can simulate a wheelchair (at least from an under-the-stall view.)

At my company we don't have any handy-capable people so the stall is usually occupied or where the reading material is left.