How to prevent an item on a fixed-item contract from sourcing to an open-item reference contract

We have several vendors who have fixed-item contracts where we also want them to have an open-item reference contract. However, we do not want the items on the fixed item contract to source to POs using the open item reference contract when the fixed-item contract is expired.

Example:

1. Enter a fixed item contract called CONTRACT1 and add two contract line items onto it: TEST_ITEM_A and TEST_ITEM_B.
2. Enter an open item reference contract called CONTRACT2 for the same VendorID.
3. Enter a requisition containing the two items and run PO autosourcing. If the fixed item contract (CONTRACT1) has not expired, the items will source to that contract. That is working fine.