Best practice for Labour Contract/Service Procurement (Work Confirmation don't support Qty based PO)

Summary:

In Our Project there is a scenario of Labour Contract, where based on skillset of the Labour a Govt. approved rate has been defined. Based on approved rate & number of hours (for a particular skillset of the labour); our client has to pay the Vendor on a periodic basis.

We observed that as per Oracle current functionality Complex PO (with work confirmation) can be used to suffice this business requirement. But as of now Work Confirmation Complex PO is only amount based.

But we want to capture the specific rate based on the skillset and a blanket hour (annual estimated hours) in WO PO. When WO release will happen, we want to capture number of working hours and system should calculate the WO release amount based on fixed rate and number of working hours.