Depending on the application server, there may be a couple of ways to get to the mbean server connector. (Note: It is not possible to get the mbean server directly remotely -- you need to go through the mbean server connector, which is almost the same thing)
Now... unfortunately, I have never worked with the WAS mbean server, so I don't know which technique is available, or best.
If the application server has a mbean server connector directly accessable, you can access it via the JMXConnectorFactory class. However, you still need to know the service URL, which is generally different for every application server that I have encountered.
IMHO, with working with Weblogic and JBoss, this is probably not the best way to get to the JMX connector. But if you find a reference to a JMX service URL, in any of the IBM help pages, you can try using it.
The recommended way is probably through JNDI -- or at least, this is preferred method for Weblogic and JBoss. Unfortunately, this means that you will have to include the WAS client jar file in your classpath. The exact calling procedure and pathname is also probably WAS specific.
You probably have to check the IBM help site to see what jar files you need, and getting a JNDI example on how to get the mbean server connector.