Return Delivery for vendor consignment stock is not possible through SD deliveries.
While creating a return PO for Vendor Consignment stock, system comes out with the message ME 640 which is an error in standard SAP. However this message can be converted into a warning one to allow creation of the return PO.
Other methods for return will be (1) with 102 movement type in MIGO with reference to the original PO
(2) 122 movement against the GR document.
Outbound deliveries against Return PO is not possible.