The idea is that you have an EJB like this:
Then, as a bridge between the Java EE world and the NetBeans Platform world, you have an application client that exposes the EJB and starts up the NetBeans Platform application...
...which contains a NetBeans module that consumes the EJB via the application client:
Once all the NetBeans Platform JARs are on the classpath of the application client, as described in the abovementioned document, you can simply run it. And the result is as follows:
Once you have your application client as described in the abovementioned document, you can do some more experimentation with calling the EJB, as described here. Reuse of existing EJBs should be pretty sweet following this approach!