If you want to sing a song in F#, one way to do it is to use two capos, one covering all six strings at the second fret, and the second (which must be a Shubb) pressing on the first five, leaving the sixth "open".

You then play the chords as if you were playing in dropped-D. You can of course move both capos up the neck to achieve playability in other keys.

You don't need a modified Shubb to do this, it is perfectly do-able using an ordinary 6 string Shubb capo.

That is the only application I can envisage using two full capos.

Three full capos simultaneously ?

I can't imagine the application, unless he was doing as I suggested above and using the third one lower down, for a bit of "patter" (as they say in Glasgow) ...

Or perhaps he wanted a dramatic key change in the middle of the song which could be achieved by releasing one of the capos ?