I thought this thread was going to be about using a SWU to free a seat in a fully booked J by upgrading a random person to F, thereby allowing your own J upgrade.

I feel I must have read about that practice in a previous thread somewhere and it's the most devious usage of a SWU I can think of.

I do agree with the idea that it in this actual scenario, it might not be possible to keep that seat free after an upgrade, short of buying it outright.