Odd policy question.

Maybe not such an odd question; Anywhoo, we have quite a few people who register our IP addresses as nameservers, and then never delete the records. I don't suppose there is any way that we can delete these old records, we have appealed to multiple registrars such as godaddy, enom, and the like to remove these bogus NS records from our IP space which keep our new customers from using these IP addresses for hosting but they claim that we have no grounds even though we are the legitimate 'keepers' of said IP space. This is mainly a problem for customers who use software such as cPanel which likes to always make NS records automatically, and customers almost never remove these at their registrar. Any thoughts? -Drew