Pricing Question - How to set up surcharge/discount based on dff

 I've read the manuals, but I'm still confused on how to do this.

We have a spoils allowance (discount).  It is stored on a dff on the ship_to_customer_site record.  It applies to the entire order amt.

If it is null or zero, then this discount does not apply. If it is greater than zero, say 1, then the customer gets a 1% discount on the entire order.

Do I need to add a pricing attribute and can it be used in a formula?

Any Help is much appreciated.