I think Ahole is right. A Volume Spinner might work better on a cabinet without touchscreen. With touchscreen, make a onscreen volume knop instead, possible with pincode protected Or use a Remote control (which normally not have such a spinner on it).
Personly no buttons should been added in a touchscreen cabinet, that is why you try to hide all buttons, unlike example my own software that was designed with buttons in mind.
Otherwice it should been pretty easy to made this features in the touchscreeen application, But warning, Z axis is far defficent than X and Y.
Arcade Music Box / MultiJuke was designed with mame arcade cabs and buttons in general, so this is why I got that idea and supported a volume spinner with a shift button (which can been disabled here).