Have you checked out EJB by OReily. I believe they have a chapter that talks about the EJB 2 and 3 beans interoperability. That might help you.
I have one doubt though, when you migrate your entity beans to JPA entities, would you be modifying the existing code base? If yes then why not take annotations?
I’ve looked at a lot of different solutions, and in my humble opinion Aspose is the way to go. Here’s the link: http://aspose.com
subject: how to migrate EJB 2.0 to EJb 3.0 using XML descriptors