[Zope] ZClasses and automatic sub-objects

I have an ObjectManager-derived ZClass. I would like all instances of this ZClass to have a subobject added to them automatically at creation time. This subobject has a fixed id in each instance (in this case, I want to add Image objects with an id of "logo"). Preferably, this object would a permanent part of each instance...you wouldn't be able to delete or rename it in any instance, but you would be able to edit it (e.g., upload image data). So, essentially it would act analogously to a property sheet. Is this even possible? I asked this question a couple of weeks ago and never got a response. -- Tim Moore