If the FAA won't play ball with inerting, maybe there's another simpler way to stop the ullage filling with flammable vapours:
"c. There seems to have been little discussion throughout the TWA800 saga about the virtues or benefits of fuel additives to raise auto-ignition flash-points (page 41). I would have thought that any improvements in this area could be achieved without loss of calorific value per unit mass of fuel. And every step in the right direction helps disproportionately. An alternative to adulterating the whole fuel load in this way might be (for "at risk" a/c) simply to add a physically immiscible heavier fraction of distillate to the CWT that would still be less dense than the Jet A, float on top of residual fuel and suppress Jet A vapours (much as a thin layer of oil floating on water stops evaporation). The quite small quantities involved would mix well via downstream filtration, when pumped into the wing-tanks, HP pump-sprayed and then atomised into the combustion chamber - and so should not unduly affect the normal power-plant combustion process. "
The basic idea is that the additive would be required (to be added by the refuellers) once the temperature exceeded a given figure -30 deg celsius say (unless the CWT was to be at least half-filled - whereby the cooling heat-sink effect would then stop the underlying aircon packs from heating the fuel sufficiently to create a build-up of vapour). I would imagine that 25 US gallons would be enough to give a one inch top-layer of "damping" additive on the residual fuel in an essentially empty 747 CWT.