Intercompany Requisitions with Blanket - OU1 Create PR => OU2 Owns GPA and Creates PO

We are in the global design phase of an R12 implementation. The client uses a GPA process whereby Inventory Org A within OU2 creates a PR which is under a GPA owned by OU3.  The PO is shipped to Inventory Org A.  However, we would like to model the scenario described within the Cost Management User Guide where the PR is created in OU2, but the PO is created in OU3 (with PO receipt happening in Inventory Org B, and subsequent shipment to Inventory Org A). 
We need to follow this model so we can leverage standard functionality to update costs in Inventory Org B based on PO.