Changing BarLine glyph per staff

[Robert Stoddard]

I am setting a piece in which different parts repeat at different points (because the repeated sections in each part are the same number of bars, this works out in the end...).  I thought this was going to be straightforward using code like this:

\version "2.13.61"
staffChoir = \new ChoirStaff {
        \time 4/4
    <<
        \context Staff = "Tenor" {  
            \relative c'' {
                c2 g \once \override Staff.BarLine #'glyph = #"|:" | 
                e c | e g \once \override Staff.BarLine #'glyph = #":|" | 
                c g | c1
            }
        }
        \context Staff = "Bass" {               
            \clef bass
            \relative c {
                c2 e | g e \once \override Staff.BarLine #'glyph = #"|:" | 
                c e | g b \once \override Staff.BarLine #'glyph = #":|" | 
                c1
            }
        }
    >>
}

\score {
    <<
        \staffChoir
    >>
  \layout {
    \context { \Score
        \override SpanBar #'transparent = ##t %Turns off staff lines between staves
    }
  }
}

But this isn't working -- all bars still print as simple verticals.  Any suggestions?

Thanks in advance,
Robert
www.bostonsing.org