Breathing marks

[Phil Holmes]

It seems a common use of the breath mark to create other markup within the 
stave: for example the finalis in Gregorian music.  I have been using it 
to place a 3 before rests in Mensural music, to signify triple time.  
However, I now have a rest of this sort that comes at the start of a 
piece, and it would appear that LilyPond does not allow a breath mark to 
start a piece.  In the example:

\relative c'' { 
  \override BreathingSign.text = \markup { 3 }
  \override BreathingSign.Y-offset = #-1
  \breathe r \breathe r \breathe r
}

we only get two threes: the initial one is missing.  Is there a better way 
of providing the 3 mark, or an override I'm missing?

Thanks.