If B and C need to exchange information, is there some reason that B can't ask A to talk to C? If that is acceptable, then A can be in broadcast mode, talking to B and C at the same time, with specific messages for each, that the other ignores. B talks to A and says "Hey, A, tell C xxxx", so A says "C xxxx". C responds "Hey, A, tell B yyyy" and A says "B yyyy".