I have thought about doing this as well. I just didn't get around to all the details before my last show. I might work on it over the winter to get it solidified. My ideas:
levels would be a great idea - Bows here are not the biggest seller for me in the larger sizes. I thought about offering 2" or 3" bows on a month basis, a clippie club and even a bottlecap necklace club. I would make sure to know when the girl's b-day is and send a special bow for the birthday. Offer a gift card that the buyer could write out and you could include with the first shipment so they could have a personal note. $$ upfront would be key. I thought about offering a solid of the month or a print of the month, but maybe that would be way too many decisions. I don't want customers to get overwhelmed. I would end up making some samples and either taking a picture of them or have them clipped to a separate board to advertise, with the disclaimer that the bows may not be of the exact same print, etc., in case you run out of the ribbon you had.