Syllable reminder

[David Feuer]

When a long melisma is broken over two or more lines, it is often
helpful (particularly for rehearsal) to indicate at the beginning of
each line what vowel/syllable should be sung.  For example, if "you"
were broken over two lines, it might appear as

             you ______
(oo) ______

Is there any way to do this in Lilypond (without using fully manual
line breaking)?  If not, what would be involved in implementing it?
Ideally, the reminder would only appear if the following lyric
extender were longer than some user-specified minimum.

David Feuer