Bonnie of Scottcrewcandlesupply.com sent in the following hack...
I have done this. I actually have 2 different types of discounts. One for special member groups and one for strictly coupon codes.
This is how I did it, these are all done in the setup file:
1. I added the extra order form fields in the setup file
2. Added the following discout related fields: @sc_order_form_discount_related_fields =
3. Discount Logic: (the first one is based on the referred_by field, the 2nd is based on the coupon_code. you can also use either a straight amount or a percentage.)
Then you should be good to go. You don't have to use both, but I thought it might be good to show that you can base your discounts on several fields.