[Zope] zClasses with zClasses - can they act in a folderish way?

Ive been experimenting with zClasses nested within zClasses. I can get all kinds of behaviours happening and its extremely usefull. What I cant seem to achieve is to get a nested zClass to display in a folderish manner in the managment tree. I can get zClasses at the top level of a product to display in a folderish way (i.e. having a '+' control to expand its subtrees), but I cant get a zClass embedded inside a zClass to display this way. Ive tried subclassing from Folder, ObjectManager, nothing, etc etc, but nothing seems to work. Any suggestions anyone?