Hi Urs,
is this what you want?
\version "2.17.26"
\relative c' {
r8
\override Arpeggio #'extra-offset = #'(1.5 . 0)
\override AccidentalCautionary #'extra-offset = #'(-0.8 . 0)
<es?
\tweak AccidentalCautionary.extra-offset #'(2.3 . 0)
c'?
as'?>8 \arpeggio
}
It is "very manual", though. As accidentals and the arpeggio are
shifted, the space between the rest and the arpeggio is still larger
than usual. Of course, you can play with the numbers. The main "trick"
is the \tweak AccidentalCautionary.
HTH,
Joram