Try mapping a MIDI Controller, such as Foot Controller (4) to the Isoharmonic Ratio Spacing selector by right-clicking and choosing Learn from the mapping dialog. Move the controller and it's mapped. Now sweep the controller while playing to change the ratios during a performance.
Sounds like this.
[Example audio file is currently unavailable.]
In the second half of this MP3 file, the controller values are drawn in by hand in the MIDI editor of Reaper, creating a step-sequenced transformation of the timbre.