I get the so called battle field upgrade quite often, I know most of the GA at my home small airport and try to mention in the nicest possible way that I am 1 on the list and boarding the plane. I am more often then not told "oh thank you for telling me if there ends up being a seat I will come get you.". Low and behold it happens pretty often. A lot of times a little kindness coupled with a smile and a great attitude goes a long way. YMMV