Try just hooking the NVGToggle event.
If they turn their NVG on, turn it back off automatically.
Code:
register_event("NVGToggle", "blockNVG", "1=1");
The 1=1 flag means the blockNVG function will only get called if the user turned their NVG on. If you did 1=2, then it would get called when NVG got turned off, which is useless in this case