You can use a dns name and create a split horizion dns where you make fogserv.domain.com at each school point locally to the local fog server.
The issue is as Wayne said, Once the client touches a fog server it becomes tattooed to that fog server. Now if you know that ahead of time you can synchronize (i.e. copy the ssl certificate from your master FOG servers to the other remote fog servers) then have the clients reach out via dns name. If you have any clients that have touched one of the older non master fog server, you will have to reinstall the fog client on the target computer.