Contracts and Change Orders

Hi,

In Procurement module, How can i achieve the below scenario of contract management.

Contract Value is 100,000 so my first PO is PO001 with original contract value..Once the contractor commences the work I want subsequent change orders to be linked with original PO so that at any point of time inquiry on that contract must show as below..

PO001 - Original Contract Value 100,000

CO001 - First Change Order on Contract 001 Value 50,000

CO002 - Second Change Order on Contract 002 Value 70,000

Original Contract Value = 100,000

Change Orders  = 120,000

Total (Including Change Orders) = 220,000

Regards