The ability to bring up Tuner via a MIDI Program Change has been requested numerous times. It has been implemented in the latest Beta version, but has not yet made it to the User manual. There is a reason these are called Beta.
How it works is that if you select Program 124, you get the Tuner. This goes through the MIDImap, so you can choose what PC (or none) does this. It operates in the same way as BYP, ACT and TOG (see [RCV.MAP] in the UM).