An easier thing to do (in 2013 only of course) is you can set the size of the queue that is used for an event. So in this case you would set the queue size to 1, and only one event will be in the queue to be handled. In the Edit Events window select the "Limit Maximum instances of this event in the event queue" and choose 1. My tests show that this seems to work correctly and the last event to handle is the last event fired.