[Zope] preventing add list pollution - how?

I knew the best practice to do that, but I forgot it, and don't find the solution on zope or elsewhere, and probably I'm confused. Say I have a container product, and objects which just will be added to that container or its subobjects. Therefore I don't want the subobjects to appear in the general add list, just in the add list of the container. I know how to manipulate that add-lists, my problem is what to do with the subobjects to get them into zope "properly". Do I write my subobjects like normal zope product, just without registering them with zope as products? Do I then add instance of my subobjects to a container just using _.setObject? cheers, oliver