returning a fault with message style

[Joel Carklin]

I am using the message style. I have the following method:
public Document processRequest(Document doc) {
        Document res_dom_doc = null;
        try {
            My_Message msg = new My_Message(doc);
            MyConnectionToExternalSystem conn =
newMyConnectionToExternalSystem("<ip_address>",8686,"comm1");
            My_Message res = conn.sendAndReceiveMessage(msg, 45000);
            res_dom_doc = res.getMsgAsDOMDocument();
        } catch( Exception e ) {
            //
        }
        return res_dom_doc;
    }

If all goes well on my external system, this works perfectly.
Sometimes the returned Document is a custom fault which I need to return
to the client as a SOAP Fault. I added this code to help:
SOAPBody sb =
MessageContext.getCurrentContext().getResponseMessage().getSOAPPart().getEnvelope().getBody();
SOAPFault fault = sb.addFault();
fault.setFaultString(whatever the string is);
fault.setFaultCode("Server");
 
But now I need to add the res_dom_doc, returned by my external system,
as a child of the <detail> element of the soap fault. Can anyone please
explain how I can do this? Using the code above, an empty detail element
in returned and the res_dom_doc xml comes after the closing tag of
soapfault ( </soapenv:Fault> ).

thanks
Joel