Purchase order with Regular items AND Subcontracted Items

In many common cases we are facing problems were we have:

-One item in the PO that requires Raw Material sent to Subcontract
-All the other items Are regular purchased items

The system as it is right now doesn’t allow to Add any other Regular items if the option:
Is selected to YES

The only workaround is doing separate PO’s for splitting the purchase for the order to the supplier.
But it’s gonna look a bit odd to the supplier.