Offer to sell packages of replacement bits. All of the flat bits wear quickly if they are used often and many of the very small diameter tools wear quickly too. I'd be glad to buy additional bits if they were offered. They are arranged in sets by type. You could just offer to sell a set of flat tips for example. There is nothing sadder than a 54 bit driver kit with the 5 most often used bits broken or missing. I can imagine your marketing folk quietly thinking - buy another set, but no I'd rather buy the needed replacements.