Using JBoss AS6, but trying to stay as container-agnostic as possible, might as well ask if that is possible though?
I'm using the JBoss default EJB version so I think that is an alpha of EJB 3.1.1 (could be wrong though).
As far as extending Properties goes, my main concern is being able to extend any class, seems kind of odd if using ejb's prevents you from using inheritance, could just be me not understanding something though?