Preventing GR from a PO

Hi,

We create standard POs (NB type) for inter company goods movements and for external vendors. For inter company goods movements, we have the inter company replenishment deliveries while but don't create inbound deliveries from the vendors in our system.

We want to have a process whereby the users can do a MIGO for the inter co replenishment deliveries only from the deliveries, not against the POs.

For the external vendors, obviously, we have to do the MIGO against the POs. Is this possible? If so, where does this configuration lie?

Thanks a lot.