While Simple-JNDI ships with an in-memory JNDI implementation, there is nothing to stop you using a different in-memory JNDI implementation, such as Apache Directory JNDI Naming or a completely different type of JNDI implementation, provided it is writable.
To do this, use the org.osjava.sj.factory property to contain the ContextFactory of your chosen JNDI implementation. For example to use Directory Naming you would do:
org.osjava.sj.factory=org.apache.naming.NamingContextFactory
If you should use the loader with a different JNDI implementation, we would love to know.