Do you mean you're using Seam Remoting to return a list? If so, it has an "exclude" attribute which you can use to restrict the returned object graph, check the remoting chapter of the documentation for usage.
No, it is a web service. I found @WebMethod also has an exclude atribute bud it is boolean and it's definition is "Marks a method to NOT be exposed as a web method.", so it's not what I'm looking for. Any idea? Thank you!