The rules of shotgun state that the driver can call one "reload" when "shotgun" has been called. This word will, in effect, null out the previous "shotgun" call and allow a second calling of "shotgun", allowing another passenger the opportunity to call. However, if the original winner re-calls it, then he may sit in his rightful shotgun position.
Note: It can only be called once and only by the driver. Remember, its your only hope when the fat bitch that smells of fish has called it.