How to route Purchase Requisition Approvals based on RequestorDefault Cost Center Segment

We need to route Purchase Requisition Approvals to specific approval groups based on the Cost Center Segment that is assigned to the Requestor's Default Expense Account. We cannot use the Charge Account Cost Center as these are balance sheet accounts, and the Cost Center will be '0000' but Requisitions still need to flow according to the Requestor assigned Cost Center.