Aligning lyrics to an invisible Voice

[Aaron VonderHaar]

I would like to print lyrics in the center of a grandstaff that are  
aligned to a rhythm that is not printed.  Here is what I have tried,  
but lilypond gives the following message,

    warning: cannot find Voice `lyricsRhythm'
    warning: cannot find Voice `lyricsRhythm'

The result is that the lyricsRhythm appears on it's own staff (I  
don't want it to appear at all); and the lyrics do not appear.

Thanks for any suggestions,

--Aaron V.


\version "2.6.4"
upper = \transpose c c' { \time 3/4  c4 e g | c e g | c e g }
lower = \transpose c c { \time 3/4  c2. | c | c }

\context Voice = lyricsRhythm {
  \time 3/4
  c4 c c | c4. c8 c4 | c2. |
}

verseOne = \lyricmode { One two three | four and six | seven }
verseTwo = \lyricmode { Eight nine ten | e -- le -- ven | twelve }

\score {
  \context PianoStaff <<
    \context Staff = upper \upper
    \lyricsto lyricsRhythm \new Lyrics \verseOne
    \lyricsto lyricsRhythm \new Lyrics \verseTwo
    \context Staff = lower \lower
  >>
  \layout { }
}