HttpWebRequest class with AllowWriteStreamBuffering support

I need a class that works just as HttpWebRequest but that supports the AllowWriteStreamBuffering property. Must compile for Windows Phone 7 (Silverlight .Net 4 C#). Main purpose of this class is to be able to upload multipart/form-data http posts but without causing memory overload on the web request stream (AllowWriteStreamBuffering = false is used to prevent this but currently not available on Windows Phone). This is why this class needed. Could also be based on sockets as long as compiles for Windows Phone 7.