Apache Axis and SAML

I've looked at the examples of calling a simple web service on the
Apache Axis website.
I've also looked at the examples of using WSS4J in conjunction with
Axis. I'm confused about how WSS4J can be used in the context of the
basic TestClient example from the Axis developer's guide (below). There
is no specific example corresponding to this.

I'd like to be able to add SAML tokens to a SOAP message, but I have a
couple of basic questions:

1. The WSS4J examples make use of a callback class to manipulate the
SOAP message. How is this callback class registered, in the context of
the example below.

2. The examples get a reference to the SOAP envelope object, but how do
I obtain this, in the context of the example below.

So, if I wanted to add a SAML user authentication token to this web
service operation call, how would this be achieved?

Thanks.

import org.apache.axis.client.Call;
import org.apache.axis.client.Service;
import javax.xml.namespace.QName;

public class TestClient {
  public static void main(String [] args) {
  try {
    String endpoint =
         "http://ws.apache.org:5049/axis/services/echo";

    Service service = new Service();
    Call call = (Call) service.createCall();

    call.setTargetEndpointAddress( new java.net.URL(endpoint) );
    call.setOperationName(new QName("http://soapinterop.org/",
echoString"));

   String ret = (String) call.invoke( new Object[] { "Hello!" });

    System.out.println("Sent 'Hello!', got '" + ret + "'");
    } catch (Exception e) {
    System.err.println(e.toString());
  }
 }
}