How to create a playback score for microtonal music?

I don’t know really how practical your workaround is – obviously it would be a lot, lot better if Dorico had some native support for microtonal playback, and I hope that will come sooner than “a very long time” – but you can create multiple layouts that contain only one instrument, and use one instrument for playback and another (muted) one for printing, if you wish.