Yes, that option with the keyboard would be the easiest option. See? The point on encrypting your whole disk is not to avoid tampering, but to lock your machine

Yes, that option with the keyboard would be the easiest option. See? The point on encrypting your whole disk is not to avoid tampering, but to lock your machine in public places and be sure that no one can access your data upon placing that disk in another machine, or even trying to boot it.