Vertical text at the end of score

[Dominique Faure]

Hi,
With the following code (mainly stolen from
http://lilypond.1069038.n5.nabble.com/vertical-text-tt31444.html), I
could get some vertical text at the end of my score:

%%%%%%%%%%
\version "2.16.0"

markVerticalText =
#(define-music-function (parser location text) (string?)
   #{
     \once \override Score.RehearsalMark #'rotation = #'(90 0 0)
     \once \override Score.RehearsalMark #'extra-offset = #'(1.5 . 7)
     \once \override Score.RehearsalMark #'direction = #DOWN
     \once \override Score.RehearsalMark #'font-size = #-4
     \once \override Score.RehearsalMark #'font-shape = #'italic
     \mark \markup $text
  #})

\score {
  \new StaffGroup <<
    \new Staff {
      R1 R1
      \markVerticalText "Some text here"
    }
    \new Staff { R1 R1 }
    \new Staff { R1 R1 }
  >>
}
%%%%%%%%%%

Nevertheless, this solution isn't fully satisfactory, since I need to
render several lines of text with some placement control on the result
(at least centered on the staff group).

BTW, is there a mean (other than altering the ragged-right parameter)
to ensure that this extra final width extend would be taken in account
while letting lilypond populate the staves on the page?

-- 
Dominique