is it possible to put a measure count in \quoteDuring?

[Kieren MacMillan]

Hello all,

I have a score which changes time signatures a lot. I have a global variable 
like this:

global = {
    \key c \major
  %%  Stanza 1
    \time 4/4 \tempoMUMM #"Flowing, rubato" #"4" "ca. 72–100" s1*2
    \time 3/4 s4*3
    \time 4/4 s1*3
    \time 3/4 s4*3
    \time 4/4 s1*2
      \tempoMU #"(moving)" s1
      \tempoMU #"(a little less)" s1
    \time 2/4 s4*2
  %%  Stanza 2  %%
    \time 4/4 s1*2
    \time 2/4 s4*2
    \time 4/4 s1 \tempoMU #"rit." s1
  %%  Stanza 3  %%
    \time 3/4 \tempoMU #"first tempo" s4*3
    \time 4/4 s1 \tempoMU #"(motion)" s1
      \tempoMU #"(retreating)" s1
      \tempoMUMM #"Deliberate" #"4" #"ca. 56" s1*4
  %%  Stanza 4  %%
      \tempoMU #"(moving a little)" s1
    \time 7/8 s8*7
    \time 3/4 s4*3*2
    \time 4/4 s1
    \time 2/4 s4*2
    \time 5/8 s8*5
    \time 4/4 \tempoMU #"molto rit." s1
    \bar "||"
}

Several of the instrumental parts have rests for (e.g.,) all but the last 6 
measures of the piece. What I would like to do is:

\addQuote #'skips { \skipsOnly \global }
fluteNotes = \relative {
  \quoteDuring #'skips { \measures #27 }
}

This is pseudo-code, obviously. But there are two functions in there that would 
be incredibly helpful in a lot of my Lily code:

\skipsOnly m
   = return only skips (or multi-measure-rests?) from music m

\measures n
   = return a moment equal to number n of full measures (regardless of time 
signatures)

In particular, the \measures function would save me rewriting (or 
copying-and-pasting) all those skips.
And if the structure of my piece ever gets modified, this would save me having 
to hunt down the equivalent place in multiple parts.

Where can I start looking for such functions (or starting points to develop 
them)?

Thanks,
Kieren.