could you give more details about the mecanism you need.
I already did such an implementation through the use of a singleton accessed by a MDB and this singleton fires a PropertyChange event to local listeners that could be other EJBs. But this only works if within the same JVM. This could be extended to remote JVM by implementation of serialized forms of my poperties to set up a "remote" Observable pattern.
So, to resume I use only one MDB to handle client message queues and this MDB references a singleton to spray changes to listeners.
Thats an idea...
hope this helps, regards,