Sebastian Bergmann has posted details (and a patch) for freezing and unfreezing objects via the new setAccessible method included in the SPL in PHP 5.3.
One of the many new features that have been added for PHP 5.3 is the setAccessible() method of the ReflectionProperty class that is part of PHP's Reflection API. This method makes protected and private attributes (unfortunately, the class is called ReflectionProperty instead of ReflectionAttribute) of a class or object accessible for the ReflectionProperty::getValue() and ReflectionProperty::setValue() methods, thus making protected and private attributes "open" for full read and write access from the outside.
A bit of code shows how to "freeze" and "thaw" the objects out - creating an object, calling the freeze() method on it to protect it from use, then the thaw() method to bring it back out where it can be accessed. Stefan Priebsch helped to create this class and the patch.