Generally i agree with Marko.
But i have seen implementation similar to what you suggest. Idea was following - master sends 1 broadcast request. After that slaves respond with some lag time. Lag time was different for all slaves, so there was only i active sender on bus at any given time.
Maybe you can implement the same - but this entirely depends on protocol specification. If it allows such communication scheme - there should be defined how exactly implement broadcast functionality. If protocol doesn't allow - sorry then it would be impossible as all slaves will respond together, thus breaking communication as Marko stated above.