Broadcasting messages to all clients listening on a specific subject is quite simple and involves nothing more than forgoing use of the reply API. For instance:

MessageBuilder.createMessage().
    .toSubject("MessageListener")
    .with("Text", "Hello, from your overlords in the cloud")
    .noErrorHandling().sendGlobalWith(dispatcher);

If sent from the server, all clients currently connected, who are listening to the subject "MessageListener" will receive the message. It's as simple as that.