If you're in flight and the aircraft is at ZFW and not in balance what is your bigger problem? The fact you're outside the envelope or the fact you have no fuel? Therein lies your answer.
I know in flight planning you check max takeoff weight, max landing weight and zero fuel weight (or at least ZFW and max takeoff weight, as landing weight's CoG will fit between the two), however where is that mentioned in the CAR, if at all? A quick search of the CAR online finds no mention of the word 'zero'.