start/stop staff

[address@hidden]

I have a quartet piece with a recitative type section in one part.  The other 
parts play, essentially, punctuation.  The "solo" part is rhythmically complex 
enough that having it on the accompanying parts would make it far easier to 
play.  I could easily put the entire movement in each part as a StaffGroup but 
I would prefer a two-line staffGroup only for the sections where the solo part 
is not homophonic with the rest.  How would I go about starting/stopping such a 
thing?

Put simply, I want to start the parts with a staffGroup which contains the 
individual part with the solo part above at a reduced size.  Then, when that 
section is done, reduce to the individual part.  Then reintroduce the solo part 
at a later section for the same reason.

TIA,

David