Remoting is used with JBossWS on the client side (the server side is deployed within a web container). I still think would be possible to make work from client side since web servers accept compress requests, however I don't know exactly how JBossWS exposes configuration for remoting within their client.
Last week I looked at the code and it looks like JBoss Web Services would require Remoting 2.0.0 with the JBREM-425 http://jira.jboss.com/jira/browse/JBREM-425;jsessionid=506E94EEC425428E9D0B647DBCB56E7C fix. The JBoss Web Services client would need to make the proper invoke call to add "Accept-Encoding", "x-gzip, x-deflate, gzip, deflate" or something like that to the HTTP header that gets sent out. Please correct me if I am wrong. Also from looking at the Web Services code it looks like the remoting configuration is not exposed.
So this can be done via remoting by adding entry in header map passed into remoting clinet, such as:
headerProps.put("Accept-Encoding", "x-gzip, x-deflate, gzip, deflate");
but don't think there is a mapping for this within jbossws (as you said). Guess can create a feature request in jira for the jbossws team.