Instead of using the offline message window provided by Comm100, you may redirect your visitors to your own page when your button is in offline status.
Log into your Comm100 account;
Click Campaign at the left menu;
Click Offline Message;
Note: Make sure you are editing the correct campaign if you have multiple campaigns existing.
Select Redirect visitors to my own page when no agents are available, and fill in the URL of your own page;
Click Save Changes.