re: "but how would I be able to hook into that invocation?"
What is the nature of your client? I don't know much about web services, so I don't know what you mean by "webservice client generated by CXF". But I can say that if you don't have direct access to the actual Remoting call Client.invoke(), I don't see how will be able to set the value of the metadata map.
"webservice client generated by CXF" means that I used a tool from the Apache CXF framework in order to generate required Java classes, including some client code, from the given WSDL. I then rely on the JBoss webservice stack to send the request. You are absolutely right: I was able to step through the entire stack in the debugger and found out that no matter which properties I set in the metadata map while I still have access to the request being prepared (there are some properties for proxy options), they are discarded shortly before the request is sent out to the target endpoint. Thus, I could not programmatically influence the proxy to be used. JBoss even ignored system properties, so I was pretty lost. In the end, the case was solved because I could use a transparent proxy by changing the host name part of the endpoint, so I didn't have to fiddle around with proxy settings any more. Thanks a lot for your reply though, it does point in the right direction