deserts != terra nullius
although jatropha *could* grow in arid parts of australia, it's almost certain that someone will complain about affecting the "delicate ecosystems"* with their many rare and endangered creatures (most of which look like mice) and plants (most of which look like grass)
i can't see this idea getting off the ground (haha), unfortunately; even if there was no barrier to filling up otherwise unsustainable australian farmland (those lost to drought, salinity, etc) with jatropha, the sheer scale of the energy requirements for jet travel make this only a tiny part of a solution - we need a denser energy source.
--
* apparently all ecosystems are "delicate" when anyone wants to do anything with them