partial shipment

Hi Experts,

we have a following scenario

we will getting the order say 1000 units with incoterms CIF (Sea freight) and the shipment is partial shipment. After despatching 500 for balance 500 units customer will insist us to dispatch by Air instead of Sea with different incoterms but prepared to pay the difference. please advise me how to configure the above.

Thanks in Advance

V.S.Aasish