I know this idea is pretty far "out there", but what if you could have an aircraft hover over the structure and spray water, rather than dump it, like a giant shower? The whole idea of using water is that, with its high heat capacity, it absorbs the heat from the fire, as well as reducing its access to oxygen, but dumping it all at once obviously is bad for anything on the ground, but maybe showering it would work? I know, it's probably not feasible.