Stanza (or similar) at the end of a line?

[Matthew Collett]

I'm typesetting a set of psalm verses with recurring antiphon, and would like 
the lyric line for each verse to end with the indication "℟." (responsum) to 
remind the singers to repeat the antiphon.  The following does not work - the 
end-of-line stanza marks simply do not appear: 

\version "2.16"

\layout {
  indent = 0.0\cm
  \context {
    \Staff
    \remove "Time_signature_engraver"
  }
  \context {
    \Lyrics
    \override LyricText #'self-alignment-X = #left 
  }
}

response =  {
  \new Staff <<
    \clef treble \new Voice = "antiphon" { \relative f { a'4 b a g a1 \bar ":|" 
} }
    \new Lyrics \lyricsto "antiphon" { \set stanza = "℟." This is the re -- 
sponse.  }
  >> 
}

verseOne = \lyricmode { \set stanza = "1."
"This is the" first verse.  \set stanza = "℟." 
}
verseTwo = \lyricmode { \set stanza = "2."
"This is the" next verse.  \set stanza = "℟." 
}

\score { \response \layout { ragged-last = ##t } }

sMusic = << \relative f {
        a'1 g2 a \bar "||"
} >>

\score { 
    \new Staff << \clef treble \new Voice = "sopranos" { \sMusic }
    \new Lyrics \lyricsto "sopranos" { \verseOne }
  >>
}

\score { 
    \new Staff << \clef treble \new Voice = "sopranos" { \sMusic }
    \new Lyrics \lyricsto "sopranos" { \verseTwo }
  >>
}

How else can this be done?  Ideally, the final "℟."s would be right-aligned on 
the final barline, at the same height (and in the same size and style) as the 
stanza numbers.

Best wishes,
Matthew