Notso,
Yes I agree, but the mass of air displaced is small. I haven't calculated air density at 35,000 ft, but I guess it will be about 1/4 of density at 8,000 ft. So aircraft contains about 1 tonne of air, and displaces about 250 kg. Nett weight of air is 0 up to 8,000 ft, increasing to about 750 kg at 35,000 ft.
This is insignificant compared with 400+ tonnes of Aluminium/Jet A1/PAX/Freight etc.
All these calcs are a bit of a futile excercise without better starting data anyway.
Hopefully someone may be able to come up with a better figure for the aircraft total volume.