I wish I could help more with your problem, but I have the same dilemma and no solution yet. Then only thing I'm really good at is coding an exe file extension. If you ever need help with that please let me know and I'll do my best to offer advice.
I would suggest to have your required entity beans to implement an interface let say
Accountable, and to use an entity listener class for the
Accountableimplementation for handling the pre persist and pre update call backs. The listener can resolve the account from the session scope via seam api easily.