One hardware fader to control two faders in Mainstage via select button

Hi,

I try to use one hardware fader von a VMK161 plus controller keyboard to control two faders in Mainstage independently. I want to use a "Select button" where I can route the hardware MIDI fader signal to either 1st or 2nd fader in Mainstage.

Any idea how to do this?

Thanks,

Keys Richards