Existing technology is capable of producing a removable trigger mechanism which can be quickly slotted into the weapon. You carry the trigger mechanism, small and light, the weapon remains in a box in the cockpit. Box can be key (similar to cockpit door), or combination changed by maintainance on a scheduled basis and the combination issued to the Capt in ops prior to flight. Weapon is useless without trigger. I.O. You may now blithley wander on your search for fodder without having to pack heat. Weapon only assembled at Capt's discretion.
Nothing is foolproof. We cannot even prevent CFIT in a perfectly good machine so there will always be ways round any preventative measure. It is simply a small step towards taking care of one element of a problem facing us that is presently of concern to many, and may afford the cockpit crew some small measure of controlling an unpleasant situation getting many times worse.