need inverted __sleep?

Hi All, hoping somebody can help me here.. I need to implement an inverted __sleep method, by which I mean to specify what variables should not be included. use case: <?php class base { private $notToBeSerialized; public function __sleep() {

    // TODO code return instance properties excluding $notToBeSerialized

} } class foo extends base { private $bar; } class poo extends foo { private $baz; } $p = new poo; echo serialize($p); ---- I've tried using get_object_vars($this), and ReflectionObject($this) both of which don't include all the properties of the instance. the only way I can see to get all the properties of the instance is to serialize($this) then parse the string, but that's just wrong and what would sleep return on the first call to serialize. any help greatly appreciated. regards, nathan