Assuming you are on an Business class AAdvantage award; your only hope is to keep in touch with AA.

If you see something like J9 D9 between a week & a few days before your flight contact AAdvantage and see if they can get QF to release a seat for your award. In the unlikely event U becomes available call AAdvantage immediately.

Aside from the extremely rare "Operational Upgrade" Qantas will not upgrade at check-in or in the lounge.