Text-spanner text repeated at start of line

[David Sumbler]

I want to use a marking such as "accel.-----al----Vivace".

However, the following example does not do what I want, because the text
is repeated at the start of each new line of music.  I just want the
dotted line to continue without repetition of the text.

\version "2.19.24"

\relative {
  \override TextSpanner.bound-details.left.text = "accelerando"
  c''4\startTextSpan c c c | c c c c | c c c c \break |
  c4 c c c\stopTextSpan |
  \override TextSpanner.bound-details.left.text = "al"
  c\startTextSpan c c c\stopTextSpan |
  \tempo "Vivace" c c c c|
}

I tried using break-visibility, but as I expected this property does not
have any with these objects.

How can this be achieved?

Also, it would be nice if the dotted line could be made to continue
right up to the next piece of text, rather than leaving a gap.

David