obviously you have not dealt with BAEC NA...

xenole, i suggest you search flights to a city that neither BA nor AA serves and check a segment between HKG and such city that will have wide open space.

for example, searching JFK to CAN would work and force only KA or CX as partner options and will not pull up any BA or AA flights. If there are no flights it is because there is no space between JFK and HKG almost all the time.

enjoy.