[Design Problem] Custom RoleProvier & MembershipProvider, dinamically assign roles

Hi, i'd like to let my site administrator to create custom roles and assign some site function to a given role. Maybe the role "office" should be able to create a new item, but not to delete it.
I know i can set the "Authorize(Role = "office")" to the delete action. But i need something more "dynamic", something like "Authorize(Role = GetAllRolesForThisAction)".
Anyone can point me to the right direction? Many thanks... 
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