With PHP 5.4, you can add setters to an object on the fly! [/sarcasm]

gistfile1.aw

class ObjectEncapsulatingState
{
        private $number;

        public function __construct($number)
        {
                $this->number = $number;
        }
}

$object = new ObjectEncapsulatingState(42);
$modifier = function () {
        $this->number = 23;
};
// $modifier = $modifier->bindTo($object); // still avoids access to $this->number
$modifier = $modifier->bindTo($object, $object);
$modifier();
var_dump($object); 
// output contains ["number":"ObjectEncapsulatingState":private]=> int(23)