EJB 2.0 : How to create complete mock of 3rd party Ejb server appliction?

I currently working on a project which communicates with a 3rd part EJB 2 application(which basically sits on top of some complex hardware). We do have the client jars with us which is the EJB client jars.

By the client jars we connect to this EJB server.

Now for testing our application we cannot use the real server and source code of server is closed too.

So here I would like to mock/stub the complete EJB server application.

One way would be analyze the code and rebuild the complete EJB server application which I feel will take quite long.

Another way could be to avoid complete mock and just for a particular unit test case mock the required EJB server parts. How we can do it and how we can prevent the code duplication here?

So what can simple and quick way to do it.