In partial accomplishment of this with text spanners, the following is close but I can't figure out how to get the rightmost Unicode glyph to sit further down, and then I also need arrows off to the right of this glyph from time to time.
I am sure others can do much better than my effort here.
Andrew
===
\version "2.19.81"
treble = {
\override TextSpanner.style = #'line
\override TextSpanner.bound-details.left.stencil-align-dir-y = #CENTER
\override TextSpanner.bound-details.left.text = \markup { \char ##x25D0 }
\override TextSpanner.bound-details.right.text = \markup { \char ##x20DD }
\override TextSpanner.bound-details.right.arrow = ##t
c'4\startTextSpan
c' c' c' |
c' c' c' c'\stopTextSpan |
}
===