Multiple freight legs for one shipment

Hi,

We are in an industry where there may be multiple freight legs for a single shipment.  Each leg would have a different vendor.

Example:

We have a 1000 ton shipment coming from Canada to the US

1) Freight leg vendor #1 brings the shipment from point A to B.

2) Freight leg vendor #2 brings the shipment from point B to C

3) Freight leg vendor #3 brings the shipment from point C to final destination.

How can we have AP pay each vendor?  Currently, they will pay the first bill they receive leaving to way to pay the additional invoices as they come in.

Thanks for your help.