Hi Martin,
I see it is not technical issue. It is business process design issue.
For temp staff who work for 1 or 2 weeks, they do not get user ID.
Usually they send an email to purchasing team and a purchasing assistant creates an Shopping Cart with own user ID. SC is approved by responsible cost center manager and PO is created. When the company receive an invoice, each requester does not need to check invoice. Because it is pre-approved before purchasing.
Please share your business process design for "Procure to Pay".
Regards,
Masa / SAP Technology RIG