Changing the SpanBar for a single staff

[Kevin Barry]

Dear LilyPond users,

I am trying to add an analysis staff above a PianoStaff group to which 
its bar lines are connected with a dotted SpanBar.  Since the SpanBar 
appears to only live in a context for staffgroups (PianoStaff, 
ChoirStaff etc) there appears to be no way to add one to a lone staff. 
My best attempt is to include the PianoStaff inside a StaffGroup and set 
different SpanBars for each one, but the result is that the PianoStaff 
prints both SpanBars on top of eachother (the code for this is at the 
bottom of the email).  My various attempts to alter the SpanBar for a 
single staff have no effect.  I would appreciate any help!

\version "2.16.1"

\score {
  \new StaffGroup \with {
    \remove "System_start_delimiter_engraver"
    \override SpanBar #'glyph-name = #":"
  }
  <<
    \new Staff { c'1 }
    \new PianoStaff \with {
      \override SpanBar #'glyph-name = #"|" }
    <<
      \new Staff { c' }
      \new Staff { c' }
    >>
  >>
}

Regards,
Kevin Barry