It's not quite as straightforward as that, but the Luminite Graviton M1 + XY joystick controller might be a great solution for you. You can stick the XY controller wherever you want and it takes barely any space. Its two 4 way joysticks + joystick press which you can assign to anything.
The M1 could go whereever you need a screen so it can show e.g your instrument on it.
You could use the M1 for this alone if e.g "pick up your mandolin, tap on a touchscreen" is a viable way to go.
A further idea would be to just use the buttons on the ML5 to turn the loops you need on and off.
Do you need to change instruments during a song by walking to one on a stand or is it "take off instrument A, pick up instrument B" between songs type deal?