BA and even AA sites do a crappy job building itineraries.

look via TYO, not actually out of your way because of great circle.

Also examine tyo-XXX-LON options - fra, hel, paris should all add some possibilities.

Also, does BA add and surcharges for AA flights between AUS/Asia and the US on avios redemptions? - consider coming home the 'full way round' - YVR-JFK on CX is great if you can get it.

Finally remember if booking a trip out of HKG to break the ticket in two as no surcharges ex HKG.

none of this is any good if wanting to use a GUF2 or 2for1 of course.