It has been asserted that a dimished seventh chord cannot be tuned in just intonation. While a composer may well want the sound of the equal tempered blur of a diminished seventh chord on the piano or organ, I believe as used by Mozart and Copper, and maybe Scriabin … one day i’ll look into that music more …, it can and should be tuned as shown. Not all composers spell the chord correctly even when used as in my example as a clear substitute for a secondary dominant.
There is only one untunable interval, the Pythagorean minor third, the same interval that falls in the dominant seventh chord between fifth and seventh. The other intervals, including the resolution major and minor seconds, have clear and unambiguous tuning.
For another example of using just intonation in contemporary music, listen to my arrangement of the beautiful folk song “O Danny Boy”. https://soundcloud.com/williamcopper/o-danny-boy
intonalist 
Very cool! What do you think about tuning the 7th of the diminished vii a minor third below the root, instead of a minor third above the fifth? Thus making it resolve down by a chromatic minor second (25/24) instead of 21/20.