how to set different line-widths for different movements within same score?

[Peter Kaplan]

I would like to set two short movements of a piece on the same page, but with
different line-widths (one movement's lines set at 18cm, the other's left to
vary with the text).  What is the easiest way to implement this, within a single
score?  Can I apply a unique
  \paper { }
block to each individual 
  \new score { } 
within a 
  \score { }
?

Thanks.
pk