Arduino based MIDI control surface

I want to make a simple MIDI control surface based on an arduino microcontroller. More specifically what I'm trying to achieve is a device like those "single channel mixer controllers", think xtouch one, faderport, cc121.

I've actually already got a MEGA 2560 programmed to send midi data and it's wired up with a rotary POT. With loopmidi and hairless midi running in the background FL Studio recognizes it completely and I can assign whatever is wired into the arduino inputs to anything I want. My problem is I don't know how to mimick the function of the "channel +/-" buttons on those premade controllers. Since I will only use one fader, I want to know how to switch mixer track focus with a switch wired to the arduino and have it automatically "pair" my one fader to the fader of that new mixer track in focus. Right now, my fader would stay assigned to whatever I paired it with until I manually change it later.