For the past year or so I've had two options for my feet with my rhythm stage setup. I can play bass:

Or I can play drums:

But when I play mandolin I want both!

I tried a system where I play bass but whichever drum pedal I tap triggers a kick as well, which sort of works but I'm not good enough at playing a consistent rhythm while moving between pedals:

This almost works, but I couldn't get it to where I was happy with it.

Another thing I tried was pulling my hand away from the mandolin briefly to change the current bass note:

This works on that particular tune which isn't very notey and it happens that each time I want to change to a new bass note the melody asks for an open string, but it doesn't work in general.

A few days ago I got another idea: allocate the left two pedals to drums (kick and snare) and the right two pedals to bass. Since this gives me three options: right heel, right toe, and both together. Since three chords is (sort of) all you need, this offers an interesting balance. Currently I have it set so I can choose between major (I IV V), minor (i bVII bVI), and mixolydian (I bVII V).

I'm still getting it into my muscle memory, but here's how it sounds so far: