Is there any way to apply a filter temporarily ?

I want to do this...


   io::filtering_ostream out;
   out.push_back(file_sink("my_file.txt"));

   out << "Authentication: ";
   
   out.push_front ( base64_encoder() );      // pseudo-code... see *push_front* instead of *push*  

   out << make_ntlm_auth_from_system();      // this have to be base64 encoded

   out.pop_front();                          // removes the base64_encoder

   out << "......";                          // *NO* base64 encoded


I don't want to do this...



   io::filtering_ostream out;
   out.push(file_sink("my_file.txt"));

   out << "Authentication: ";                            

   out.pop();

   out.push(base64_encoder());
   out.push(file_sink("my_file.txt"));

   out << make_ntlm_auth_from_system();     

   out.pop();
   out.pop();

   out.push(file_sink("my_file.txt"));

   out << "......";                         

The function make_ntlm_auth_from_system() creates an object that is *OStreamable*.

Any other suggestions are welcome. :)

Thanks and regards,
Fernando.