How do I link a requisition value set to procurement contract numbers

Summary:

Requisition value set that pulls through procurement contract numbers from that module. User can select one for information purposes.

Content (please ensure you mask any confidential information):

Our client would like a DFF on the requsition line so the user can select a procurement contract (from a LOV) that the requsition links to. This could be a contract that does not have a purchase agreement, so is not linked that way. I can't seem to see an option to add this to a value set. I believe this might need some SQL to pull it through from the table in the value set, but am unaware of what this is /how to do it, and found nothing on MOS or CCC. Thanks