\score {
  \new ChoirStaff {
    \relative c'' <<
      \new Staff {
        \time 12/8
        \stemUp
        c4. d8 e8 f g4 f8 e8. d16 c8
      }
      \new Staff {
        % hides staff and notes so that only the grid lines are visible
        \hideNotes
        \hide Staff.BarLine
        \override Staff.StaffSymbol.line-count = #0
        \hide Staff.TimeSignature
        \hide Staff.Clef
        
        % dummy notes to force regular note spacing
        \once  \override Score.GridLine.thickness = #4.0
        c8 c c
        \once  \override Score.GridLine.thickness = #3.0
        c8 c c
        \once  \override Score.GridLine.thickness = #4.0
        c8 c c
        \once  \override Score.GridLine.thickness = #3.0
        c8 c c
      }
    >>
  }
  \layout {
    \context {
      \Score
      \consists "Grid_line_span_engraver"
      % center grid lines horizontally below note heads
      \override NoteColumn.X-offset = #-0.5
    }
    \context {
      \Staff
      \consists "Grid_point_engraver"
      gridInterval = #(ly:make-moment 1/8)
      % set line length and positioning:
      % two staff spaces above center line on hidden staff
      % to four spaces below center line on visible staff
      \override GridPoint.Y-extent = #'(2 . -4)
    }
    ragged-right = ##t
  }
}