How about

{
  \key ces \major
  \bar ".|:"
  \grace \tweak extra-spacing-width #'(-1 . 0) as'8 \glissando
  ces''2
}

How about

{
  \key ces \major
  \bar ".|:"
  \grace \tweak extra-spacing-width #'(-1 . 0) as'8 \glissando
  ces''2
}

or

{
  \key ces \major
  \temporary\override Staff.BarLine.space-alist.first-note = #'(fixed-space . 6)
  \bar ".|:"
  \grace as'8 \glissando
  \revert Staff.BarLine.space-alist.first-note
  ces''2
}

How about

{
  \key ces \major
  \bar ".|:"
  \grace \tweak extra-spacing-width #'(-1 . 0) as'8\tweak minimum-length #3 \glissando
  ces''2
}

How about

{
  \key ces \major
  \bar ".|:"
  \grace \tweak extra-spacing-width #'(-1 . 0) as'8 \glissando
  ces''2
}