Copying text from carrier into PO

I have set up the following process. I linked the standard partner role CR carrier to the vendor master and the purchase order to make carrier determination possible.

Meaning in my vendor master I added a carrier, meaning when I create a PO for that vendor the carrier will be assigned. Now I have a text on carrier level "shipping instructions" which I would like to see on my PO. But when I create my PO and I check the header text "shipping instruction", the text from the vendor is copied and not the one from the carrier.

When I check customizing I can define all kind of copying rules but I'm not able to refer or set up a copy ole based on partner roles.

Is there a way doing this without enhancement?

Thanks

Walter Goris