Not that this would work on an ES and I don't have wheel pants on my RG Legacy, but I work as a builder for X-Air which is a light sport. We have a small hole in the pant just aft of the bolt. We then take some safety wire and wrap it a few turns around a small washer (probably about a #6) and then put both ends through the hole. You now have one end of the safety wire secured and can use the ends as you normally would to secure the bolt head using a ANxH- bolt
Dan