/// <summary>
    /// Returns the list of all discounts which should be applied to the specified shopping cart item.
    /// </summary>
    /// <param name="item">Shopping cart item</param>
    protected override List<IItemDiscount> GetDiscountsInternal(ShoppingCartItemInfo item)
    {
        List<IItemDiscount> discounts = base.GetDiscountsInternal(item);

        if (discounts != null && item != null)
        {
            foreach (IItemDiscount discount in discounts)
            {
                if (discount.ItemDiscountType == DiscountTypeEnum.DiscountCoupon && discount.ItemDiscountID == "<YourDiscountCouponID>")
                {
                    discount.ItemDiscountedUnits = 1;
                }
            }
        }

        return discounts;
    }
}