Refurb sub contract PO one material two line items

Hi we have the following scenario:

We have a sub contract (item category L) for a rotable spare. We create a service PO for the MATERIAL. When the invoice comes in there are two line items as we charged for materials used to repair the item at one tax rate, and the service to replair the item at another rate.

How do we goods reciept / SES this to ensure that we only get stock of one coming back in from the vendor but capture two lines in the invoice to ensure that the invoice doesn't block? So we can't create a two line item PO as the goods reciept would book two into stock.

Any suggestions?

Thanks hope this makes sence.

Other things that might help:

Single item recursive BOM

Goods issued to vendor via ME20

Legal requirement to have two lines as we are paying two rates of tax