Hi,
Why you need a separate purchase order for planned delivery cost?
You can have a (ZDEL)delivery condition type for planned delivery cost with condition category B(M/06). Add this condition type ZDEL to your MM pricing procedure and keep an account key* in Accrual column(M/08). Assign a G/L account with that account key* (OBYC).
Create PO with Main vendor( material supplied vendor) and add delivery vendor (if required) by clicking delivery condition type in PO itself(ME21N)
Carry on Goods receipt for that PO(MIGO) and can separately go for invoice verification for Main Vendor and Delivery vendor(MIRO)
Regards,
Biju K