Have you considered looking at the JBI facilities within GF? Because that's essentially what you're talking about, and JBI will do what you want.
Simply, you set up a BPEL script (which is an XML artifact) to lay out your processes, and the JBI engine uses that script to move internal messages around through interested Session Beans. It will do this using a single transaction, and can use the local calling semantics for internal Session Beans.
In the end, you use the BPEL designer tools in NetBeans to maintain the XML file, so that keeps this kind of orchestration away from actual Java code.
It might suit your needs, or at least be a platform to better explore what you may want without having to invent any new wheels on your own.
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