Well, game end and winner is actually determined by a python script, so a modder can set whatever victory conditions he wants
Thus he could devise a set victory conditions completely unrelated to flags or even ticket numbers.
A silly example, but there were some FH1-derived maps intended for a very similar gameplay: first jeep which completes 5 laps with at least 2 players on it wins the round.
So you shouldn't consider my question in the context of a standard unmodded game, it's more of a "does BF2 allow any changes to its vanilla behavior on this matter?"