Originally Posted by
beckoa
In theory, one can also upgrade to F for cash during OLCI or at the gate if there is upgrade space (cost varies based on flight distances). The price is per passenger. This is not very common anymore as most upgrade space is taken by elite members.
This is what sort of what I was considering or as ashill eluded to pay the fare difference. In my case U space was not available. Also, and I'll check my fare class, I did not buy up as F seemed full (from seat chart) so any chance of a down stream upgrade seemed minimal (using point/cash/or whatever).