Possible solution -- turn Local MIDI off, route MIDI to connected iPad, re-route reconfigured MIDI back to Rev2, with THRU going to your 2nd board. MIDIflow is a very flexible app, and can split / remap / filter / re-assign all kinds of MIDI events.
Of course you could try this trick to see if it works --Split the Rev2, but set the volume to 0 for the side you will use to play the other instrument. Rev2 allocates voices dynamically, so it might work good enough depending on what you play.
Ok I finally found a ridiculously simple solution using Ableton.Create an instrument rack with 2 external instruments.Split keyboardEndCan't believe I struggled so long on something so simple.Just when you think you know Ableton...