Add a vertical line to TextSpanner

[Thomas Morley]

Hi,

I'm trying to add a vertical line to the left side of a TextSpanner.
This line should connect the TextSpanner with the middle line of the
StaffSymbol.

Here a manual done example code:

{
  \once \override TextSpanner.bound-details.left.text =
    \markup
      \with-dimensions #'(0 . 0) #'(0 . 0)
      \draw-line #'(0 . -2.85)
  b1\startTextSpan
  b1\stopTextSpan

  \once \override TextSpanner.bound-details.left.text =
    \markup
      \with-dimensions #'(0 . 0) #'(0 . 0)
      \draw-line #'(0 . -4.5)
  b1\startTextSpan
  b''1\stopTextSpan

  \once \override TextSpanner.bound-details.left.text =
    \markup
      \with-dimensions #'(0 . 0) #'(0 . 0)
      \draw-line #'(0 . -5.7)
  b1\startTextSpan
  b''1^!\stopTextSpan
}

Could this be done automagically?

Thanks,
  Harm