I was unclear in my OP. What I want is that every keystroke on Account 1 gets mapped to a specific key to client B & C.

i.e. I type my random crap in guildchat in client A, and it' sends '1' to B & C.

Playing the AH on B & C while playing my main toons on A. '1' contains a confirm post macro on B & C.

(if I was to enable keybroadcasting that would result in just cloning what I do on account A to B & C, which is not what I'm after).