2 Boxing a FP is going to be a feat just short of epic. "Could" it be done? well, Im sure at some point, someone will work out all the fight timings, and custom make a boxing profile that is perfectly efficient. However, given the current state of the game, lack of macros, lack of FTL, lack of IWT, Healing being a custom job, companions being so heavily gear dependent, I would steer clear of FPs at level. Now, I did take a couple near level 30 toons and a third level 12 through BT, and completely smashed faces until the level 12 is geared with all options from the FP. That definitely made things easier when I moved on with the level 12.

Point is, there are ways of making things happen, just depends on how much effort and time a person wants to invest into doing it for the sake of "doing it".