Dashed line with text spanner

[Vaughan McAlley]

Hello,

I have a text spanner with a dashed line indicating an accelerando. How do
I get the dashed line to begin and end just a bit further away from its
text?

Vaughan

%% Example start
\version "2.25.29"

\relative c'' {
  \time 4/4
  \override TextSpanner.bound-details.left.text = \markup { \small \bold
\upright "accel." }
  \override TextSpanner.bound-details.right.text = \markup \small \bold
\upright \concat { "a tempo " \note {4} #UP " = 104" }

  c4 c c c |
  c4 \startTextSpan c c c |
  c4 c c c |
  c4 c c c |
  c4 \stopTextSpan c c c |
  c4 c c c |
}
%% Example ends