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The first thing I do when I book QF gift vouchers (which are just dummy bookings) is log on to the BA my booking page (ba.com) just using the booking/voucher reference and your surname. Once you're on your 'booking', in the list of options on the page there will be one to add your frequent flyer information. Add your QF number and you're done, this is also a good way to add such info for compensations and other messed up bookings.
The gift vouchers are dummy bookings for the lesser known Qantas flight QF9090, from Winter Haven to Vichadero
(GCMAP).
Once you've added your QF number onto the booking you should immediately find it now listed on the QF my bookings when you login with your QFF#. Sneakily the QF computer recognises the cunning combinations of airports as a gift voucher. Clicking View/Change takes you to the voucher booking page. This way you never lose track of your gift vouchers!