Route in PO automatically

Hi All

I have requirement that when user creates an standard NB intercompany PO the Route field under Shipping tab at item level should get filled up automatically. could any one please guide me on the same. Currently In SD deliveries it is coming because a Z table and a user exit is maintained for the same.

The solution of having the field mandatory is not what is needed. It should pick up from somewhere.If i try making an STO it is picking from config in logistics excution under Route determination procedure.

Please help with any document or config requirements.