Add Discount Section to Purchase Order

Hi! It would be nice if we could add a discount section to the purchase orders that does not go to the product tracker.
I always create POs before I start ordering, and then once I order the items, I ensure the PO matches the Invoice given to me by the vender.
Well, sometimes those invoices now contain line item Discounts that must be entered on the PO to make the final purchase amount accurate. These discounts then go to the Tracker.
I hope this all makes sense.
Thanks for considering this request.
Destini