Which version of JBoss are you interested in? I believe in JBoss-5 (which is in CR1 and not stable), because of the new VFS implementation, there's a way to specify a user-defined folder, containing class files, to be added to the classpath. There's a jboss-structure.xml which can be used to do this kind of stuff. I have not yet tried it.
We're currently using JBoss 4.2
Could you point me to some literature that outlines (or details) what you've mentioned?