Interesting, I emailed the following to the list but for the first time ever it was rejected by the list moderator (person or software?) for being too large, yet it is not. Anyway, I mention here Karim Haddid's help for me, and sure enough, he has also posted. I'll copy the text ere, and send the PDF to you personally off list to avoid this strange problem.
Currently I do not
have a lot of time to look into your problem, but this does remind me of
work I have done for my current String Quartet engraving. It's a New
Complexity composition by a colleague (all 300 pages of it) and some
parts are in polymeter and in different tempos. Here attached is an
extract of one of those sections, which demonstrates a system comprised
of four instruments with staves that end at different positions - two
duos. This reminded me of your score.
If of interest, I can send you the code for this privately.
can find out about how this is done in the NR under the polymeter
section. It involves a subtle use of scaled durations. I must also
acknowledge Karim Haddid who helped me very much achieving this result. I
will say in advance that setting up the proportional ratios for this
section involved a large amount of thinking (and headache tablets).