Discount in MM Purchase order

Hi I am in the agri business. Currently we purchase produce from vendor1 at 10USD per TON.

I need that those 10USD go to inventory cost. This was answered in another thread and its ok.

When executing MIRO I need to discount 1USD per received TON from vendor 1 and give that 1USD to vendor2 for each received TON.

So my cost for produce is 10USD per ton

Vendor1 receives 9USD

Vendor2 (its like a growers association) receives 1USD per TON.

Tried to do this as delivery cost but the result is adding that 1USD, so at the end I am paying 11USD per TON: 10USD to inventory cost and 1USD to delivery costs which is wrong.