Carrier at the Requisition level

We are release 12.1.3. Currently when user need to expedite an order we tell them to utilize the need-by-date and note to supplier  While this works most of the time we’d like a more clear cut solution to express how an item should be shipped. There is a field on the PO called “Ship Via” that we can set-up Freight Carriers to give us the choices of Ground, Standard Overnight, Priority Overnight & First Overnight .  We’d like a field on the requisition header so requesters can select it and then populates into the header of the PO since we don’t touch most of the POs.