Tonytales,
couldn't even use high pressure nitrogen to assist as you needed to be able to add fuel and ignition to combust the air to give it an energy boost for the start.
Indeed the B707 air bottle was charged with nitrogen on all aircraft I worked on. As I previously mentioned, normal air starter not combustor starter was used.. The air bottle was only filled with air when using the onboard re-charge unit, if fitted.
TW