Vendor Account Numbers

I have a client who is using one set id but has 2 entities and is sharing the vendor master. Each entity has a unique vendor account number that they want printed to the PO. I know that I can use the location tab on the vendor setup to make two vendor locations however that leads to duplication of the payable and procurement setup because they have a centralized AP. Does anyone have any other suggestions on where to put vendor account number that could be easily pulled into the PO based upon the business unit?