How to force tempo markings on single line

[H. S. Teoh]

I'm generating parts from an orchestral score, and am running an issue
where long tempo markings over collapsed multi-measure rests would force
the text to stack up in an ugly way on top of each other. Is there some
way of telling lilypond to prefer stretching the horizontal width of the
bars instead? Almost minimal example:

        \version "2.18.2"
        \score {
                \new Staff {
                        \set Score.skipBars = ##t
                        \tempo "Allegro con moto" 4 = 120
                        R1*8
                        \tempo "Adagio sostenuto" 4 = 50
                        R1*8
                }
        }


T

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