I generated the impl and server Java code for the particular example I am using: http://anonsvn.jboss.org/repos/riftsaw/trunk/samples/quickstart/simple_correlation_header/bpelContent/HelloGoodbye.wsdl
I didn't find any difference between the generated code with and without the "-exsh true" option. Although the appropriate I am using is the Provider class, though looking at the generated code might provide an indication of how cxf is different - but no luck :(