If you act with respect, you will get respect.
1.)If you convince the checkout person, that your important, they will treat you like it.
I was flying from JFK to France. I convinced the laidy that I am a tour organizer and I was very tired.
Then told her an upgrade to all seat flat business class upgrade would really be nice. It worked.
2.) Tell the checkout person, that the first leg of your flight was horrible. There was this huge man sitting next to you and you couldnt sleep! Make them have Rachmonos on you, and it could work. Did for me.
3.) Just walk up to the gate and ask if there are any empty first class seats. Tell them it would really be nice to have one. Did that from atlanta to ny.
These are all person to person tactics, which can work, if you do it right. Remember to do these tactics with a huge smile.
Good Luck!