>Can you create a "Discount" item:
>
>Item F, Qty=1, Rate=-615, Total=-615

Wouldn't that screw up the sales reports? This thing of yours has a quantity...

I've seen guys do that (me too, early on), and they always had to have some special handling for this sort of item.

The two regular ways around it were already shown in this thread: either recalculate the prices in each line item, or have one lump sum discount as an additional field on the invoice.