Automatically adding extender lines in lyrics

[YTG 1234]

Hello,

Often, multiple voices in a score have the same lyrics, or the lyrics 
have repeating components (such as lines from a poem). Is there a way to 
automatically add extender lines to melismata in the lyrics?

I found this old project: 
https://github.com/lyp-packages/auto-extenders, but, at as far as I can 
understand the code, it adds extenders indiscriminately to /every/ syllable.

I think the best way to go about this is to check whether the note or 
chord in the associated voice at the same musical moment as a lyric has 
a shorter duration than the lyric, and add an extender if it does. 
Alternatively, perhaps one could emulate the manner in which Lilypond 
itself detects melismata (by slurs, manual beams when auto beaming is 
off, or by the \melisma command).

I would appreciate some help with actually implementing that, as I don't 
know enough about Lilypond internals to do it by myself.

P. S. I found an old (~2007) message on the lilypond-devel list, asking 
for something similar, though it doesn't appear to have any replies.