Welcome to FlyerTalk, Makinco.

As you've already been advised, by both AA and eponymous_coward, it's not possible to do what you want to do. Unless you have a very good reason for wanting to be on the BA non-stop flight, however, remember that a redemption on AA metal will be cheaper in cash terms than one involving BA fees/charges.

More generally, long-haul flights in economy/coach are not usually an especially good use of miles.