I actually managed to do this on a WEATHER bump.

Flight from BOS-IAD was cancelled due to weather at IAD. I was trying to get to RIC, and was planning on renting a car when I got to Dulles and driving the rest of the way, because a flight directly into Richmond was like $600 more.

Anyway, all flights into IAD were cancelled for the rest of the day (and there were like 5 of them) and the agent was frantically trying to rebook everyone. I nonchalantly said "Hey, um, is there any room on the flight to Richmond, or to Norfolk? I can fly there instead." She was so relieved to be done with me, when I asked if she could just change the whole thing to an RIC roundtrip, she did it in a heartbeat.

I was in Richmond two hours before I would have been originally, and I got to stay longer because I didn't have to drive back to IAD to fly home, all because I offered an easy fix to the nightmarish situation the agent was in.