Service Debrief - Discount Items

Hello,

We have business scenario where Discount is provided after completing the Service. User do not want to change the Actual Amount instead want to add Line for Discount (Negative Amount).

We have an option to add the Discount Line manually after Order Creation. But we are automating Submit Charge Lines (Order Creation) and Order Booking.

In Debrief we cannot add Negative Amount. I'm thinking of the following solution: Capture Discount Item in Debrief > And in Charge Lines update the Amount to Negative Value using Custom program. 

Please suggest if there is any other possibility.

Regards,

Chakry.