Special layout for a score : four hands

Hi, all!

Some time ago, Werner asked on the devel-list in a thread about "setting the number of pages for a score"

My main concern is to make
lilypond handle the above described situation automatically --
lilypond's normal page breaking algorithm won't work because the left
and right page for `primo' and `secondo' have be handled
synchronously. Here an example of the distribution of bars. The even
pages are on the left.

   page secondo primo
   ---- ------- -----
     2 1-40 --
     3 -- 1-40
     4 41-70 --
     5 -- 41-70


Of course I can manually insert \pageBreaks, but... Just to be sure:
Have you ever seen such primo/secondo scores?

And we have today the question from a French user.
Has anybody achieved this? Or, at least, has anybody any hint about where to put the fingers?