parenthesizing arpeggios

[Urs Liska]

Dear listers,

I thought it should be simple and straightforward, but I don't 
understand how to put an arpeggio in brackets.
If I use this code I only get a very small parenthesis:

\version "2.15.36"
\relative c' {
  %\once \override ParenthesesItem #'font-size = #6
  <c g' e'>-\parenthesize \arpeggio
}

If I use the (commented out) override, I get a much bigger parenthesis 
but this doesn't work at all, because it is too wide and round.
Is there a possibility to put brackets around objects and let the 
brackets adapt to the height of the objects (like spanners)?

Thanks for hints
Urs