What is the best way to do "Possession" Receiving ahead of final destination?

The scenario is as follows...supplier(s) are contractually required to deliver materials to a freight-forwarder who will export the materials to their final destination. Buyer ownership of the materials takes place at that point, so the supplier can invoice and be paid. The materials are considered as en-route from the moment they left the suppliers facility to the moment they arrive at the final destination. There is no tracked inventory at the freight-forwarder. So, the question is how do I perform a "possession" receipt when the freight-forwarder confirms custody so that the materials can be 3 way matched to an invoice,