How to enter small fragments of alternative lyrics for a voice?

[Michael Kallas]

Hi,

I am trying to enter a collection of SATB pieces in which I've 
encountered a problem: At certain positions, I have 2 voices going
tra- la- la- la- la- la- la,
but the other two go:
tra- la- la- la- la- la- (rest) tra- la- la
For the rest of the piece, the lyrics are identical, so I don't want to 
draw two lines of identical lyrics.
Is it possible to have "blanks" in lyrics which become matched to notes?
I didn't find any way to do this in the manual but must admit that I'm 
really new to lilypond.
I'm using version 2.2.6 on Debian unstable, if that matters.

Thanks for your help
Michael Kallas
P.S.: Sorry, I'm not subscribed.