A friend of mine (a humble blue) got upgraded from Y to F. He was upgraded to J at the gate. During the flight a cabin crew spilt a tray of drinks on him and they therefore moved him to first. This was on an a380 so he made the most of it.

A second friend arrived at the gate after closing. They let him on after he protested but as there were no more seats left he was upgraded to J. When he got to his seat there was another guy there. The guy said he had a first class ticket but wanted to sit next to his friend who was in J so they swapped tickets and my friend got the F seat. All this just for turning up late at the gate.

Ok these aren't technically upgrades to F from Y but it goes to show it can happen.