title: Add filename and length parameter to WCF stream when Transfermode = Stream
body: <p>In contrast to all the SO posts that talk about this topic, I'm not interested in wrapping a stream object in a <code>[MessageContract]</code>, since that is not permitted when in <a href="http://msdn.microsoft.com/en-us/library/ms731913.aspx" rel="nofollow">streaming</a> mode (afaik).</p>
  
  <p>When I'm in streaming mode, how do I return to the client some metadata, such as length and filename?  Can I add a WCF/SOAP header?  How would I do this?</p>
  
  <p>I am looking into extending the filestream class and add a <code>[MessageHeader]</code> attribute, but I'm unable to get this to work.</p>