Tempo marking within margins

[Nick Payne]

Is there any way I can force a tempo marking to be within the margins, other than by making it a markup instead. Using keep-inside-line for PaperColumn and NonMusicalPaperColumn doesn't do it:

\version "2.17.11"

\paper {
ragged-last = ##f
}

\relative c' {
\override Score.PaperColumn.keep-inside-line = ##t
\override Score.NonMusicalPaperColumn.keep-inside-line = ##t
\repeat unfold 20 { c4 }
\tempo\markup{\bold{Largo,}\tiny{absolument attenué}}
c1%^\markup\bold{Largo, \tiny{absolument attenué}}
}