RMI (EJB3) calls between JBoss EAP 4.x and JBoss EAP 5.0

Issue

• We have two applications running, on two different instances of jboss 4.2 communicating via RMI. We are upgrading one jboss instance (the one that acts a server and hosts ejb3 session beans) to Jboss 5.0 but, for certain reasons, we want to keep the other one (the client side) running 4.2.
• As it is. I am getting class cast exception java.lang.ClassCastException: javax.naming.Reference on getting obj ref from the remote JNDI and casting it to my class.
• Adding jbossall-client.jar from 5.0 to the server/<server name>/lib folder did not help.
• How would I make it work? What is the best way to add 5.0 RMI proxies on the class path of the app running on 4.2?
• Calling EJBs on EAP 5 (eap5) from EAP 4.3 (eap4)
• Can my EAP 4.x (or earlier) deployments communicate with EAP 5.x deployed EJB3s using deployment isolation?
• EAP 4 to EAP 5 EJB3 Communication?
• Is it possible for an Application running on an old Community JBoss 4.2.3, to connect to an EAP 5.1.1 via external Naming Context and EJB3 calls?