Entering A Transport Cost Reduction in PO

Hi,

We are facing a the following special scenario with POs

Item Description	Price	Qty	Value
XXX	1	1,000	1,000.00
Transport Cost			(100.00)
Total PO Value			900.00

The transport is carried out by our own company and there fore we making the payment to the supplier after deducting transport charge

The PO approver need to see the Transport cost reduction at the point of approving PO.

Could someone please suggest a workable solution on this.

Thanks