Receipts for Contractors Purchase Orders

Hi,

I have the following requirement from a customer:

- Contractors work for the company and enter time in OTL.

- Procurement raise Requisitions to request the Contractor Services in iProcurement and Purchase Orders are created and then Received in iProc

My customer wants to be sure that only receives the PO for the amount corresponding with the time effectively worked  by the contractors.

Is there any functionality, integration or enhacement that allows to do that?

Thanks,

cv