Recently on a 3 class 777-200 I got my GPU upgrade of W fare at 36 hrs before flight but only middle seats left. At ORD Polaris lounge I asked about buying an upgrade to F. I figured free to ask. Anyhow, I was offered $600 and 30K miles. I would have done it but the computer would not let them take my money. F was empty. The nice Polaris lounge person called the gate and asked them to get me an aisle seat if it became available. So at gate someone got upgraded to F and I got their aisle seat. I was satisfied with the outcome.