I'm not exactly sure as to whether or not this works on all elevators, but...
If you aggro a mob and kite it all the way to an elevator, once you get to the top and hop off, its path will glitch and it will become stuck in place.
If you try to hit the mob, it will simply "evade" and stay in place.
Imagine kiting giant world elite mobs onto the elevators... hilarity ensues ;]
I stumbled upon this purely by accident while leveling in Netherstorm. However, I attempted to re-enact this many times, and almost every time was able to achieve the same results.
The best part about it is the fact that, after I resumed leveling for two more hours, I ran back to town and the mobs were still bugged out on the elevator.
We can assume that this works for all elevators.
It is a SERVER-SIDE BUG. Everybody can see it.
Stormspire Elevator (Netherstorm): CONFIRMED
Mechanar Elevator: CONFIRMED
Zangarmarsh Elevators: CONFIRMED
Shattrath City Elevators (Terokkar Forest): CONFIRMED
The Great Lift (Barrens/Thousand Needles): CONFIRMED
Serpentshire Cavern Elevators: CONFIRMED
Thunder Bluff Elevator (Mulgore): CONFIRMED
SCREENSHOTS: