cross-staff slur

[Helge Kruse]

Hello,

I would like to add a slur to this kind of arpeggio. Since it is written 
in both staves of the Piano Staff I can't use the parentheses. Can you 
tell me, how to write nice slurs above and below this arpeggio?

Thanks,
Helge

\version "2.12"
\include "deutsch.ly"

global = {
        \key c \major
        \time 4/4
        \set tieWaitForNote = ##t
}

one= \relative c' {
        \stemUp
        r4 g'16 ~ h ~ e ~ c ~ <e c h g>2 |
}

two = \relative c {
        \clef bass
        \set tieWaitForNote = ##t
        cis,16 ~ as' ~ f' ~ c' ~ <c f, as, cis, >2. |
}

\score {
  \new PianoStaff <<
    \new Staff << \global \one >>
        \new Staff << \global \two >>
  >>
}