Hi! is there a way to Pan 100% L, C, R with buttons?

Sorry if this is easy but I couldn't find how to do it.

I've been working on a monitor controller layout with bigger buttons for an Asus Nexus 7 and I wanted to include that for panning a mono signal to one of my Mixcubes. If I use a rotary knob it's hard to return to the exact center.

Thanks!