I have never flown on BA before. I have 2 award tickets from AA in premium economy in September LIN-LHR-MIA. The LHR-MIA segment is on an A 380. I'd like to sit in the 2 seats on the outside on the upper deck. Unlike award flights on AA, I am not able to get a seat assignment now for the BA flights, I have to wait until 24 hours when I check in. By then all the desirable seats will be gone and I could get stuck in a middle seat. Can I pay something t o BA now to reserve seats in advance or do I have to wait until check in. I am AA gold, nothing with BA.