I just ran a test and everything worked as expected.
To publish the wsdl from the proxied service on the proxy, download the wsdl, fix up the locationURI to point to the proxy, put it on the classpath, and add this bean to the servlet context...
<int-ws:inbound-gateway id="proxy" request-channel="toOutbound"/>
<int:channel id="toOutbound" />
It's then available as
<ws:static-wsdl id="thewebservice" location="classpath:my.wsdl"/>