No as the ear is a hiearchical type system. jboss5 will move towards a class loading model that can support this, but until then its not practical.
I have been digging around the JBoss API documentatin and come across the UnifiedClassLoader and LoaderRepository files.
I don't suppose there is a hack to basically connet to Jboss (using a jmx client) and tell it to load the cached MyClasses.jar?
In this case I would not update the application.xml