It is not possible to add another framework layer below PFE. This is because, objects in PFC refer to PFE objects and/or inherit from them. An example would be any DW service. If you create objects in the corporate layer by inheriting from PFE DataWindow service objects and add functions to them, they can not be accessed from u_dw since pfc_u_dw is referring to the objects placed in PFE, not in your corporate layer objects.