Capture cost from Sales Order to WBS

Hi Experts,

Now, our customer set a PS structure to control all the expenses of the different business units (BU). To the sales order some discount (cost), they want to capture to the WBS of the corresponding the project. In business language, each BU has a budget structure to manage their expense. To some of the sales discounts of the BU, the customer also consider it as cost, e.g. special discount, under WBS budget control. How can SAP PS and SD handle it? Thanks experts.

Regards,

Kenneth Yip