We had to do something similar once flying AQ-DL-DL. With elite on DL we could have up to 70lb. but AQ had a 50lb. limit. So we had to transfer some stuff from one bag to another upon check-in w/ AQ to prevent paying the feee. No big deal really since the overweight bag was 52lb. I can see how this can be a problem though, but I don't think there is any solution to it. I'm not sure if AA waives the luggage fee even for their own elites.