Apply discount in total sales order amount, not changing unit selling price

Hello Guru's

There is requirement from our user, that discount must be apply in sales order total, not based on individual line

(by applying discount and will change unit selling price).

Example:

Customer sending PO with total 10 items with specific price in each item, and total amount all is $1000. In Customer PO, they indicate 1% discount

for amount total  $1000. They expecting in SO line, will have additional line item to deduct amount which is -$10. Invoice total become $990

without changing unit selling price. Anyone have experience for this kind of request? really appreciated your feedback and comments

Thank you

Made S