subcontracting process with services

Dear All,

please guide about the below requirement from business...

1.We will be sending X material to subcontracting vendor of valuation Type "OLD" as component

2.We will receive X material with valuation type "NEW" from the vendor as finished product.

Now the issue is, users wants to specify the services to be performed for each component.

we have service master records, how to include services to be performed  in subcontracting PO?

if we add one more line item in the PO ,with item category D when we create service entry sheet the value is posted to different cost object, how to post the amount to subcontracting material.?

Thank you.

Regards,

Rahul