I am in the exact same situation. My AONE5 originated in CAI and I used two stopovers in LHR and FRA before heading to North America. I have an open dated segment to DXB that I want to use sometime after I return to Europe from Australia. Since AA RTW made all the reservations and handled the ticketing, I am considering making the reservation for this last segment directly with BA, as I figure I stand a better chance of it slipping through that way. Do you think I have a shot?