[Zope] getting base classes's (super class) _properties tuple

Say I have a fully functional (and more importantly, working) Product will call A. I want to extend this Product's capabilities so I wish to derive another class from it, call it B. No problem, class B(A): ......... now in class B I want to add a new property. Is the a way of getting the base (super) class _properties tuple and just adding the new one to it. Since a tuple is an immutable object I can't do this: _properties=A._properties.append({'id':'RenderStandardHeader', 'type':'int','mode':'w'}) Any thoughts ???? DR