How people are getting to your program. Are they coming via a website, or is it a direct link to the GT program?
If it's a direct link to the GT program, you should be able to simply erase the content of the program and replace it with
Anyone who runs the program will be automatically redirected to the program reached by this link. This will, however, create a "Please wait while we redirect you" GT message and loading screen while the program redirects.