Embedded Jetty: How to set the JMX port in source code

We have system tests and when they start an Embedded Jetty boots via the setup. The Embedded Jetty includes a JMX server, too. Then we have tests which must connect to the JMX Server via:

JMXServiceURL url = new JMXServiceURL("service:jmx:rmi:///jndi/rmi://:<JMX_PORT>/jmxrmi");
JMXConnector jmxc = JMXConnectorFactory.connect(url, null);

The problem is we cannot connect from the tests to the JMX server when we do not know the JMX port up front. Has anybody a clue how to specify the JMX port up front when the Embedded Jetty is built within the source code? The system property stuff is of no help here.