As far as can remember from earlier discussions (also here), the mechanism used by core nodes (link, status, catch, and complete) is not available to contributed nodes. This is not likely to change, since the message-passing mechanism is both deeply embedded in the core code and likely to evolve to handle distributed implementations of NR and messaging between different instances of NR and different hosts.
Simulating broadcast is clearly a reach for NR. It is contrary to the concept of sending messages on wires, which is the foundation of the tool. A flow-based programming model may not be the right answer for applications where broadcast predominates and a pub/sub architecture might be preferable.
