Hi Necr0tic,
Full Trust is a bad practice. You don't need it for 99% of cases. Why you are doing it is unknown, but assuming you are in the 1% case ...
You can't suppress the dialog for the digital certificate version of Full Tust. However, you can create a client side MSI for your XSN that installs Full Trust and when this runs there will be no pop up. InfoPath 2003 had RegForm which created the MSI. In InfoPath 2007, you have to do it through Visual Studio. Good luck!