How to reference agreement across multiple Procurement BU

Summary:

We have several Procurement BU, each with one or multiple separate Requisition BU assigned via Service Provider Relationships.

No BU is enabled for both Requistioning and Procurement.

However, in one of the Procurement BU, some global agreements are created.

The requirement is that the requisition BU from a different Procurement BU can also reference these agreements, but process via their main assigned Proc BU. I.e. 'order Locally'

See below

Even if I add additional service provider relationship between Req BU 2 and Proc BU A, it only allows me to assign the req BU 2 to the agreement.

It does not allow any way to process the orders via Proc BU B. Order Locally option is disabled.