Well... you caaan, but it requires some skill at social engineering. I did it just yesterday. Its not really honest, and you do put yourself at some risk at the airline noticing what you did and doing something like kicking you out of their frequent flier program.

The easiest is of course if the airline is at fault for something. An example of this is a friend of mine had a flight attendant accidentally spilled coffee on him mid flight. He took the opportunity to complain about it and essentially told them that now he needed to not take his flight for x and y, and that their option z will not work and why.

People make exceptions, but you have to give them a good enough reason to.

If have enough skill telling stories, and perhaps a good poker face, acting skill, and status, you can get away with a lot.

Just don't be upset if it doesn't work =P