Smart Coupons for WooCommerce

Now there is only the option to exclude coupon from products on sale. I would like to have the option to have the coupon valid if a product is on sale but only to add the difference of the discount. Etc. I have a product on 20% discount and a customer has a coupon code for 30% discount I want the coupon code to still be valid but only add the difference to the product. In this case 10% extra discount would be added to the sale discount. If the coupon code is less than it can not be added and the coupon still stays valid for the customer to use another time when there are no products on sale.