Cash Collection agent to be included in billing document

In a Scenario where there is a Agent who delivers the goods to the end customer and collects the cash and this has to be recorded as an entry in the final billing accounting document.

How to achieve this.Please note that the COD details will be known only during Delivery creation and not during sales order.

More Details below

Customer A

Cash Collection Agent B

The accounting entries are expected as below when the billing document is posted

Can the Partner function help in this situation?