Vocal scores with extra staves

[Andrew Bromage]

G'day.

I'm trying to typeset a work where one of the outputs is a vocal score.
One of the pieces involves the chorus singing in unison and then in
parts.

This is a cut-down version of my current attempt. There are two problems
here: First, the new staff isn't where I expect it to be; I'd like it to 
be part of
the ChoirStaff. Second, the lyrics for verse 2 don't start on the 
correct beat.

Any ideas?

The real example is much more complicated than this, obviously, but this
illustrates the problems.

Thanks,
Andrew Bromage

\version "2.18.2"

timeline = {
     \time 4/4
     { s1*2 } \bar "||"
     { s1*2 } \bar "|."
}

choirVerseI = { \relative c'' { c4 c c c c c c c } }
sopranoVerseII = { \relative c'' { c4 c c c c c c c } }
altoVerseII = { \relative e' { e4 e e e e e e e } }
tenorVerseII = { \relative g { g4 g g g g g g g } }
bassVerseII = { \relative c { c4 c c c c c c c } }
pianoRH = { \relative c' { <e c'>1 <e c'> <e c'> <e c'> } }
pianoLH = { \relative c { <c g'>1 <c g'> <c g'> <c g'> } }
lyricsVerseI = \lyricmode { la la la la la la la la }
lyricsVerseII = \lyricmode { lu lu lu lu lu lu lu lu }

\book {
  <<
     \new ChoirStaff {
         \clef treble \key c \major
         <<
           \timeline
           {
           \new Voice = "chorus" { \choirVerseI }
           <<
             \new Voice = "sopranoChorus" { \voiceOne \sopranoVerseII }
             \new Voice = "altoChorus" { \voiceTwo \altoVerseII }

             \new Staff {
               \clef bass \key c \major
               <<
               \new Voice = "tenorChorus" { \voiceOne \tenorVerseII }
               \new Voice = "bassChorus" { \voiceTwo \bassVerseII }
               >>
             }
           >>
          }
       >>
     }

     \new Lyrics = "chorusLyrics"

     \context Lyrics = "chorusLyrics" {
         \lyricsto "chorus" { \lyricsVerseI }
         \lyricsto "altoChorus" { \lyricsVerseII }
     }

     \new PianoStaff <<
       \new Staff { \clef treble \key c \major << \timeline \new Voice 
{ \pianoRH } >> }
       \new Staff { \clef bass \key c \major << \timeline \new Voice { 
\pianoLH } >> }
     >>
  >>
}