change alignment of Lyric with extender

[Kieren Richard MacMillan]

[ Lilypond 2.8.1 ]

Hello, all!

I tweak some of the lyrics in my piece(s) to make the note spacing a  
little more pleasing -- I have even defined some presets, e.g.,

    lyrLH = { \once \override LyricText #'self-alignment-X = #-0.5 }
    lyrRH = { \once \override LyricText #'self-alignment-X = #0.5 }

which means "align this syllable halfway to left-aligned" and "...  
right-aligned", respectively.

This is working fabulously, EXCEPT where the lyric has an extender  
(__), in which case an override like "lyrRH" has no effect (i.e., the  
syllable remains in the default position, fully left-aligned).

Can anyone tell me how I can override the alignment of an extended  
syllable?

Thanks,
Kieren.