Changing Harmony mix level on HarmonyG during song

I realize this may not be possible since the knob is a global setting not saved as a preset function but..... this is the only one of all the features I could suggest as an improvement.  I don't trust using a toe to rotate the knob in real time.  I typically use Harmony at about 9:00 to 11:00 and it works well under my voice but on some (typically driving the end of a song) cranking it would be great.