Vertical spacing again

[Werner Arnhold]

Hi list,

I work on a folk song with 4 stanzas. There is a combined staff for
women and one for men. Between them there should be the song text.
"strf" are the lyric lines for women, "strt" those for men. It looks
like that:

\score {
  \new ChoirStaff <<
    \new Staff <<
      \new Voice = "sopran" {
        \voiceOne
        << \global \soprannoten >>
      }
      \new Voice = "alt" {
        \voiceTwo
        << \global \altnoten >>
      }
    >>
    \new Lyrics = "strfI"
    \new Lyrics = "strfII"
    \new Lyrics = "strfIII"
    \new Lyrics = "strfIV"
%%%%%%%%%%   Vertical distance at this place
    \new Lyrics = "strtI"
    \new Lyrics = "strtII"
    \new Lyrics = "strtIII"
    \new Lyrics = "strtIV"
    \new Staff <<
      \new Voice = "tenor" {
        \voiceOne
        << \global \tenornoten >>
      }
      \new Voice = "bass" {
        \voiceTwo
        << \global \bassnoten >>
      }
    >>   
    \context Lyrics = "strfI" \lyricsto "sopran" \strophefI
    \context Lyrics = "strfII" \lyricsto "sopran" \strophefII
    \context Lyrics = "strfIII" \lyricsto "sopran" \strophefIII
    \context Lyrics = "strfIV" \lyricsto "sopran" \strophefIV
    \context Lyrics = "strtI" \lyricsto "tenor" \strophetI
    \context Lyrics = "strtII" \lyricsto "tenor" \strophetII
    \context Lyrics = "strtIII" \lyricsto "tenor" \strophetIII
    \context Lyrics = "strtIV" \lyricsto "tenor" \strophetIV
  >>
}

For reasons of better readabilty I want a vertical space between the
verse for women and those for men without changing the other spacing. Is
there a simple way to do that? I supposed that the vertical spacing
commands affect all lines.

Thanks in advance!

Werner