These fioriture should be played as a single ornamental entity. They should never be divided in such a way to 'make it fit' better. For example, in the opening paragragh of the Solo in Chopin's E minor concerto, there are several of these fioriture. We find one for the r.h. of 21 notes in e harmonic minor with l.h. playing (in 1/8 notes) a B7 chordal accompaniment in 3/4 time; 21:6. The six quaver B7 chords of the l.h. are played in time, while the 21 note fioritura sings in E harmonic minor with utmost fluidity. Supplesse!
We could (rightly and preferably) divide it as 21:6 or for ease of execution (7:2 + 7:2 + 7:2) would be acceptable; but never as (6:2 + 7:2 + 8:2) nor (8:2 + 8:2 + 5:2). The whole point of the fioriture is to maintain plasticity of melodic line; any attempt to make it easier by dividing it into rhythmically elementary segments will destroy the intended effect.
I imagine this would be an easier task for the human voice than the fingers.