stretching ragged last bar in the Voice context

[Federico Bruni]

I'm trying to stretch a ragged last bar in a score.
I know I can use the following override (NR 4.5.1, Known issues):

\paper {
  ragged-last = ##t
}

\relative c'' {
  \repeat unfold 4 { R1*4 \break }
  \override Score.NonMusicalPaperColumn.padding = #20
  R1 R1
}

However, I need to apply this kind of override in a Voice context, so I 
can't use NonMusicalPaperColumn.
There's any other workaround to achieve what I want?

Thanks
--
Federico