How to define global blanket agreement and use it in self service requisition catalog?

Summary:

How to define global blanket agreement in BU1 (LE1) and use it in self service requisition catalog belonging BU2(LE2)?

Content (required):

Customer has 3 legal entities, one of them making blanket agreements with suppliers and all procurement BUs and Requisition BUs will use it while creating requisitions. All procurement BUs will create POs using this global agreement and supplier will invoice to the LE crating the PO. Customer does not want any inter company transaction or any central procurement and invoicing among the companies. They just want to add this global blanket agreement to requisition and procurement catalog, so that it can be used by all the self service requisition users of different BU- LEs.