Interesting thought......
I tried that when the TA was attempting to get D seats released (Oz domestic no less) by QF in the process of issuing my current RTW.... Eventually cleared but with no regards to status as Mrs WF ticket (NB QF)
c leared first.

My process in the USA with AA as I attempt to maintain the right to "semi-elite" service (PS) at the QFF call-in desk will be to leave my AA number in the reservations and then simply ask for the FF number to be removed for a specific segment. Keep the boarding pass w/o a number and fax with ticket copy to the QF desk for credit. Only have to deal with two A class flights (albeit with connections I don't want credited to QF) so hopefully that will work. And if there is a mistake - both segments will be blank - not credited to the wrong account. To QFF's credit they seem to post this way a lot faster than AA so it may not work effectively the other way round. Shame QF have so seriously devlaued their program benefits.

YMMV

Happy wandering
WF