Drawing extenders for the full duration of a note

[Lucas Werkmeister]

Hi everyone,

I’m transcribing an old choral score for LilyPond (full source at [1]),
and while I’ve been mostly successful so far, one thing I haven’t
figured out yet is the extenders. In the original score, several notes
have extenders in the lyrics, to indicate the duration of the note
relative to the other voices, and those extenders span the full duration
of the note (see [2] for an example). This short snippet can be used to
test the behavior:

<<
  { c'1 r } \addlyrics { o __ }
  \relative c' { c8 d e f g f e d c4 g' c,2 }
>>

The second voice ensures a certain minimal width for the whole bar, and
I would like the extender in the lyrics for the first voice to span this
whole width, as that’s how long the note is. I can get close to this by
manually tweaking the LyricExtender’s minimum-length (if there’s no rest
after the extender, even setting it to +inf.0 works, it automatically
terminates at the next lyrics), but I’d prefer a solution that doesn’t
require eyeballing a close-enough value.

Cheers,
Lucas

[1]: https://github.com/lucaswerkmeister/il-est-bel-et-bon
[2]: https://i.imgur.com/9GQ0cJH.png