To disable the buttons on the front bezel of your classic open the CommBox side menu using the double arrows on the left or right of the screen. Select the cog wheel from the side menu.
Once this menu is open select the icon with the 3 lines (4th from the top). Here there will be an option for 'keypad lock' to be enabled. The power button will always remain functional as a precaution but all other buttons will now be disabled.