It is possible to pass methods to session_set_save_handler()?

While trying to encapsulate PHP4 sessions in a class I have found a problem trying to pass
methods instead of pure functions to session_set_save_handler().

This is a sketch of the relevant part of the class:

class Session {
    function open() { whatever; }
    function close() { whatever; }
    ....
    function Session() {   // constructor
     /************ Set my own session save handler ************
      If the handlers were pure functions the call to set my handlers
      would be:

      session_set_save_handler("open","close",...);

      But they are methods of this class, so what I need is something
      like this: 

     session_set_save_handler("$this->open", "$this->close",..); 

      Of course it doesn't look like it could work this way.
      Is there any solution?
      *****************************************************************/
      session_set_save_handler("?????","?????",..);
      session_start();
    }
}


Jose Saura