outgoing partial payment with cash discounts

Hello experts,

My client wants to post an outgoing partial payment (F-53) but wants to post a discount as well.

For example: 1000 € is the total value of an open item to a vendor. He want to clear 500 € of the open item being 400€ the value of the payment + 100 € the value of the discount made by the vendor.

Since F-53 doesn´t have cash discount at the partial payment screen tab how can this be made?

Best regards