[Zope] Local Roles - taking away further down the tree?

Hi there, First, AFAIK local roles are acquired further down the tree - if I assign a local role, the user will have that local role in that folder's children too. Is is possible to "remove" the local role of a user in a folder/set of folders further down the tree? If this is not possible and maybe even a stupid idea, please fire away - I need some ammo to convince the client that this is anyway not a good idea - even if it cannot be done! Thanks Etienne