There is no problem keeping the water/meth container full...I have run six or eight times in an afternoon at a local track and only used 2/3 of a gallon. Under normal use I add a couple of pints a month.
Now this is wild and exotic, way out of the box...
How about a container that is charged with cold air from the compressor via a switched pump with primed outlets in the throttle body. The air is captured during run ups...and then force fed into the throttle body during runs maybe controlled by the VEC, and when the meth is injected, the captured cold air is also force fed...while it would not be the total source of air, it would be cool enough to lower the intake temperature during a quarter mile scamper...
Just trying to think out of the box...