Here I am with a preliminary reply.
Yes, the jbossws-cxf.xml is for the deployment endpoints only and is used by jbossws integration to allow controlling details of the endpoints declared through standard means (web.xml). Its contents are added as child context to the one created using the Apache CXF defaults (which means you can still provide a cxf.xml in the deployment, be sure to put it where CXF classloading mechanism can see it, e.g in WEB-INF/classes if using war archives).
Assuming you really want to use a CXF client in your deployment, you can simply have a spring bean descriptor (call it something different from cxf.xml -say client.xml-) with the client only declarations. Then you create a SpringBus pointing to that descriptor and use the bus to create the client the cxf way.
Soon I'll have a look if there's a way for tuning the JAXBContext as you need without having to go through the spring beans declarations.