Perhaps, you just need to use a service like no-ip.com
. It's free from what I know. Generally, here's what you need to do:
1. Register with no-ip.com and create your own DNS name.
2. Install the No-ip client program on your GMS computer so that it regularly updates your DNS record with new IP address when it changes.
3. IMPORTANT: use your DNS name in the Host and Viewer settings for the custom Internet ID server (replace the IP address with your DNS name).
With this trick you won't have to change Viewer or Host settings each time your GMS IP address changes.
Hope that helps.