Customer Agreement using both Price per Part and Price per Sales Group

I would like to execute a customer agreement with both a deal per part at a set unit price, and a deal per sales group for a percentage discount. Trouble is the part is a member of the group, and I don’t want the group’s %discount to apply to that part’s unit price. Aside from entering all the other group members individually, is there any setting or other structure I can use to fetch only deal per part (net price) for this one SKU, and deal per sales group (% discount off) for the other SKUs in the group. Example: SKU1 net price $500, SKUGroup discount 20%; order line applies 20% discount to $500 and returns $400.