To answer your first question: No it's not possible to use extended scope for persistence context. Extended scope is initiated by EJB's, which in turn need a container. So extended persistence context is per definition container managed.
In that case you don't need to join transactions either, but I'm not 100% sure if I'm right about that one.
posted 5 years ago
I'm sorry but I'm totally wrong on this. Chapter 7.7 of the specs made me realize that.