There aren't any others in Europe in the present schedule once you do LHR-DXB-LHR (BA has other long-haul using 767/777 but they are excluded by DXB). AA does operate 777 domestically and sells the F seats as D, twice a day DFW-MIA and once a day ORD-DFW. Used to also be LAX-DFW but not sure if that is still operating, so that is another way -- to get real international F which is considerably better than international J on LA even if you get the coffin config. As for maximizing your mileage, you can add at least 5K to it by optimizing the US portion (something like JFK-SJU-LAX-DFW-ANC-DFW-LAX) but presumably you had reasons for visiting those specific cities in that sequence.