Thanks for all the help so far.

I managed to use the 'one flight at a time' trick and instantly upgraded my outbound flight! Prior to reading the hint here, I assumed both flights were unavailable to upgrade, so 1000 thank yous....

Now if I could only get BA to answer the phone so I can import my AA FF# and select a seat. Have been on hold for 20 minutes (after calling back after being on hold for 15). The customer service (at least for US-based non-elites) is challenging, to say the least.