make text span a specified musical interval?

[Jace Toronto]

Hi all,

This is the basic gist of what I'm trying to do:

\version "2.18.2"

\score { \new Staff \relative c' {
  \repeat volta 2 {
    c4^"vamp" r2 d8-"(Last time only)" e |
  }
  f g a4 r2 |
} }

However, the "last time only" instruction spills into the following measure, 
which makes it less clear what it refers to.  I would like for the first 
measure to be expanded to account for the width of this text.

This is simple to do if the text need apply to only one note:

\score { \new Staff \relative c' {
  \repeat volta 2 {
    c4^"vamp" r2 r8 \textLengthOn e8-"(Last time only)" |
  }
  f g a4 r2 |
} }

But for multiple notes, this does not work as intended:

\score { \new Staff \relative c' {
  \repeat volta 2 {
    c4^"vamp" r2 \textLengthOn d8-"(Last time only)" e |
  }
  f g a4 r2 |
} }

Ideally, I would like the eighth notes engraved as in the first example (as 
they are by default, with no extra space between them), but then the rest of 
the measure after them to be padded with space to account for the text, as in 
the second example.  Alternatively, the eighth notes could be spaced out a 
little more to account for the text, but having the second eighth note AFTER 
the end of the text. as \textLengthOn does by default, is ugly.

The closest thing to a solution I could find in the list archive was a clear 
description of the problem in Lilypond-internals terms 
(http://lists.gnu.org/archive/html/lilypond-user/2008-08/msg00527.html) but 
only a hint at a solution insufficient for me to figure it out.  Anyone willing 
to offer a bigger hint?  Thank you.