Another lyrics problem

[David Sumbler]

%%%%%%%
\version "2.19.48"

<<
  \new Staff {
    \relative {
      c'2 d4 e | f1 |
    }
    \addlyrics { First set of words; }
    \relative {
      g'4 f e d| c1 |
    }
    \addlyrics { se -- cond set of words. }
  }
  \new Staff {
    R1*4 |
  }
>>

%%%%%%%

The above works as I would like it to, except that the second set of
lyrics appears below the lower stave even though they are correctly
lined up with the notes in the first stave.  Further sections of music
with lyrics appear lower still on the page.

I have tried many different ways of getting what I want (some involving
"\new Lyrics" and "lyricsto"), but I can't get the result I want.

The reason for wanting to split the music and the lyrics in this way is
because the piece I am setting falls naturally into a number of
sections; but they are not separate movements, so I want the music and
the staves to be continuous.  I like to split things up so that I can
use variables and includes to compile only the section(s) I am working
on - this speeds the process up when I am checking the validity of my
input.

The actual music isn't a problem: I can control this using variables:
e.g.
flute = { }
flute = { \flute \fluteSectionOne }
flute = { \flute \fluteSectionTwo }
flute = { \flute \fluteSectionThree
}
etc.

and commenting out as desired.  But I can't get this to work with the lyrics, 
so I am having to include the lyrics with the music of each section.

Can somebody show me a working version of the above?  And/or a way of piecing 
together lyrics using variables?

David