Single buyer for multiple Orgs

Hi

I am trying to map the following business scenario in E Business R12.2

1. We have a single buyer for 3 Manufacturing/Inventory Orgs under a single Operating unit - Buyer1 and Inventory Orgs IS1, IS2, IS3.
2. The buyer has Zero approval limit for Expenses and 10000 USD limit for Raw Materials
3. When Buyer1 approves creates and approves an expense PO for IS1, the PO should go to Manager1 who runs IS1.
4. Similarly, when Buyer1, creates and approves an expense PO for IS2, it should go to Manager 2 and when Buyer1, creates and approves an expense PO for IS3, it should go to Manager3 who runs IS3