What Aaron suggested seemed to work with the passage similar to the previous
rit-a tempo example, but the stretching 8-notes problem arises elsewhere, like
in the example below.
\version "2.18.2"
pocoaccel = \markup { \italic "poco accel." }
common = {
\override TextScript.extra-spacing-width = #'(0 . 1.5)
\override TextScript.extra-spacing-height = #'(1 . 1)
\override TextScript.staff-padding = #1
s1 ^\pocoaccel
}
oboe = \relative c''{
g8 (a b c d) g, (b c) a1
}
\score {
\new Staff <<\common \oboe>>
}