When submitting a vendor invoice to the workflow, it would be good to have the option to create a work item for the purchase orderer or the person that generated the purchase order receipt.
In a normal business scenario, if the purchase invoice line fails because of a price discrepancy, the buyer would be responsible for reviewing the invoice.
If the invoice line fails because of a quantity discrepancy, the person who received the purchase order line should be reviewing the invoice.
There is no way at present on the vendor invoice / vendor invoice line workflow to assign a work item to the purchase order orderer or receiver.