I actually managed to sneak something into the EJB3 spec at the last minute to make it possible to detect a concurrentaccessexception. So the current issue is here:
I suggest that you simply add your own handling for this exception in a servlet filter or something.
Yeah, in thinking further on this issue really serializing requests would be evil.
What we really want to do is keep the browser from submitting subsequent requests. Sounds like a JSF hack to me right now.