Hi,
I think you should be able to lookup the EntityManager using JNDI.
Try to define a resource reference to EntityManager first in you war deployment descriptor web.xml, then do JNDI lookup, this may help
http://blogs.sun.com/pblaha/entry/how_to_use_entitymanager_api.
As far as I understand the Persistence Unit annotation injection is scoped to the containing EAR or WAR. What you referred to as facade isn't really a facade, it's perfectly right to CRUD through a manager EJB. I don't see a point why you wouldn't manage your entity using a session EJB that's already deployed as ejb-jar.
BR,
Mohamed
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