Many websites offer discounts to their regulars. You could mimic this specific behavior by automatically applying a coupon code to checkout baskets of regulars,

Many websites offer discounts to their regulars. You could mimic this specific behavior by automatically applying a coupon code to checkout baskets of regulars, with some text explaining how much you love them. Of course, you might want to let users know that you do this, and that means emailing them, and that makes this more of an emailed coupon offer, which is back to being more like a traditional coupon approach, but either way hopefully you can give your regulars some warm fuzzies.