I've been playing with diminished chords as 'V' in ii-V-1 progressions. I often use one of the three diminished chords in a ii-V-1 progressions - I sharp the 5th note of the scale and hang a diminished over it. So in C major I would use G# diminished for V which is really a rootless G9 so I can understand its dominant function.
But I've just been trying Eb diminished and it sounds dominant too but I don't understand why. (I've been playing 'Almost like being in love', and Eb diminished sounds great over 'being'). I then tried the only remaining diminished chord and it too seems to provide a adequate 'V' function, although it's not as nice as the other two in this context.
So, I'm wondering. Can you use any diminished as 'V' anywhere and get away with it, and is my use of Eb diminished over 'being' (i.e. V) a standard substitution? And how does it work?