How to override bar line?

[Fairchild]

Maybe this snippet/example would be worthy of enshrinement somewhere in the docs, if only there is a way to get a thin-thick bar line under the fermata at the end of the first line. Suggestions?

                              - Bruce

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  \version "2.4.6"
  \layout{ indent = 0 linewidth = 3.5\in }
  \relative c'' {
c1
 \repeat volta 2 {
\bar "||" \mark \markup { \musicglyph #"scripts-segno" }
a2 ( f~ }
 \alternative {
{ f ) c \bar"||" }
{\hideNotes \grace{ f4 ( f4~ } \unHideNotes f2 ) \bar "|." }}
\override Score.RehearsalMark
   #'break-visibility = #begin-of-line-invisible
\mark \markup { \musicglyph #"scripts-ufermata" }
\break
 \repeat volta 2 {
\bar"|:" b2 ( d~ }
 \alternative {
{ d ) c }
{\hideNotes
 \grace{ \slurUp d4 ( \stemDown d d~ c c
   \slurNeutral \stemNeutral }
 \unHideNotes
 d2 ) g,2
 ^\markup {\huge \italic \halign #0 "D.S. al Fine"} \bar"||" }}
  }

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