Ha! Big "duh" moment here. Somehow in trying to think of some sly Max solution I forgot that Ableton had implemented multiple MIDI assignments.
Thanks to all who answered. There is indeed a native solution.
@Andro yes that works, although if you set the range to off=0 and on=126 then the device will turn back on at the onset of the fader being moved and so you have the whole fader range to adjust the track's volume with the device on, which is how I'm going to do it.
Thanks guys, and sorry for the dumb question!