I'm interested in the same matter. I'd like to develop a test tool that list all the session beans that are still in the app srv but unreferenced, and that can clean them up.
Stateful session beans are removed by JBoss after a certain "time-to-live". This can be configuared in the container configuration in the jboss.xml (or standardjboss.xml) file. The default is 30 minutes i think.