How to apply discount list discount rules only once to the sales order header total

Summary:

We have a critical requirement to apply 'All Items' discount rule from discount list only at sales order header and not at all lines. This is because when a large order is created and invoiced, the invoice has multiple lines for each item on the sales order for the discounts. For example, if there are two discount rules applicable and a sales order has 2 lines, the invoice generated has 6 lines - for each item on the order, there is a line for price and two lines for the discounts. This is unacceptable as the client expects orders with