Text Spanner, with Text left-aligned to bar-line, and spanner line right-aligned to subsequent bar-line?

[Zenaan Harkness]

G'day, FP here.

Here's my code:
capoVHalf = {
   %\context { \Score \override RehearsalMark #'self-alignment-X = #RIGHT }
   %\override TextSpanner #'(bound-details l X) = #0
   %\override TextSpanner #'(bound-details right X) = #40
   %\override TextSpanner #'(bound-details right padding) = #-20
   %\once \override Score.RehearsalMark #'self-alignment-X = #LEFT
   %\once \override TextSpanner #'(bound-details left
stencil-align-dir-X) = #LEFT
   \once \override TextSpanner #'to-barline = ##t
   \once \override TextSpanner #'dash-fraction = #0.6
   \once \override TextSpanner #'(bound-details left text) = \markup {
\tiny { "½ Capo V" } }
}

It seems I can align around a bar-line, if I just use a text Mark, and
can only align the text (rehearsal mark) to a note if I want a spanner
line, eg for a guitar Capo marking, with the line extending over the
bars that the capo applies to.
This is standard notation for guitars.

I can right-align the spanner line as seen above ( #'to-barline = ##t)
by moving the corresponding \stopTextSpan to _after_ the subsequent
note to which it really applies, but at least it looks right.

But I can't get the text left aligned to the start of the bar in which
it appears; it always aligns around the center of the note to which it
follows.

Any one know if it's possible to achieve proper Capo notating with lilypond?

Thanks in advance
Zenaan