Serial Number input Before Receiving

Specific use case of selling serialized items before they are received into stock. 

My client sells serialized items that offer long lead times and thus sell what they have on purchase order. Specifically, they sell a particular unit with a particular serial number, and gaining visibility into this would be a huge planning and fulfillment resource. 

The recommendation is to allow visibility of serial numbers on Purchase Order in order to place a Sales order for a particular serialized item. 

They sell almost all items using the Special - Serial Number method, serial numbers are critical in their business, especially with the nature of their high-value individual products. Right now, in the system, Serial Numbers can only be assigned and tracked after the products have been authorized during the "Receive" stage of the PO. It would be much more beneficial if serial numbers could be assigned/tracked prior to the product being received.