Mix / Node Composite Volumetric Materials?

Hello all,
I have recently been experimenting with the volume materials functionality in Blender, as well as the material node compositor. I tried to have a simple mixer switch between two volumetric materials, but it would appear they do not work in the compositor.

Is there any way to use volumetric materials with the material node compositor in order to mix them? If not, is there a way to do this aside from creating an animation between the two (by creating a keyframe for each parameter changed?). My desired end result is to set up a single parameter/slider that will transition between two volumetric materials. An even greater possible goal it to perhaps even have multiple volumetric materials that I can set ones each “strength of influence” like one does with shapekeys.

Thank you all for your wonderful help,
Tyler