StaffGroup bar line problem in polymetric notation

[Libero Mureddu]

Hi all,
I'm working, once again, on a polymetric score and I have the following problem:
starting from the example from the 1.2.3.4 section of the doc, "Staves
with different time signatures, unequal bar lengths",
I tried to group all the staves in a StaffGroup, and, reasonably, Lily
added a Group barline.

Then, I added a StaffGroup context in which I removed the  "Span_bar_engraver".
Until here everything is fine :-)
However, as one can see in the attached file, all voices meet each
other at a certain point, and before that note I'd like to have (for
sake of clarity) a Group bar crossing all staves.

Conceptually I guess that probably I should then remove the \remove
"Span_bar_engraver" when I need it again, but I'm a bit confused about
how to do that, or if there are better solutions.

Thanks a lot,

Libero


%%% Lilypond example

\version "2.11.49"

\layout {
       \context {
         \Score
         \remove "Timing_translator"
         \remove "Default_bar_line_engraver"
       }
       \context {
               \StaffGroup
                \remove "Span_bar_engraver"
       }
               \context {
         \Staff
         \consists "Timing_translator"
         \consists "Default_bar_line_engraver"
       }
     }

     % Now each staff has its own time signature.

     \relative c' <<
     \new StaffGroup <<
       \new Staff {
         \time 3/4
         c4 c c |
         c c c |
         c8
       }
       \new Staff {
         \time 2/4
         c4 c |
         c c |
         c c |
         c8
       }
       \new Staff {
         \time 3/8
         c4. |
         c8 c c |
         c4. |
         c8 c c |
         c8
       }
       \new PianoStaff <<
            \new Staff { \time 6/8
            c2. |
            c |
            c8}
            \new Staff { \time 6/8
            c2. |
            c2. |
            c8}
          >>

       >>
     >>
%%% end of example

-- 
Libero Mureddu
Vanha Viertotie, 21 as 417
00350 Helsinki
Finland
http://liberomureddu.blogspot.com/
http://www.myspace.com/liberomureddu