change staff within chord?

[lfanele]

hello list,
how would i change the staff within a chord (it is important that the  
necks keep connected across the staves? the \change Staff command  
doesn't work within the chord < ... >.

here is my sample code:
/////////////////////////////////////////


\version "2.6.3"

#(set-global-staff-size 20)

\paper{
topmargin = 0\cm
linewidth = 10\cm
leftmargin = 0\cm
}

\layout {
        \context
        {
        \Lyrics
           \override LyricText #'font-size = #0
        \override LyricText #'font-shape = #'regular
        }
}


% o = { \change Staff = oben \stemDown } % wechselt auf anderen Staff
% u = { \change Staff = unten \stemUp }

o = { \change Staff = oben \stemDown }
u = { \change Staff = unten \stemUp }

oben =

{
\key c \major
\time 4/4


\stemUp
% < \u d f \o b>8 this won't work
<d f b>8  r % put d and f on lower stave
<e g c'> r % put e and g on lower stave
<e g cis'> r  % put e & g ...
<f a d'> r  % put f % d ...
|

}


unten =
{
\clef bass
\key c \major
\time 4/4

\voiceTwo
g,8 r c, r a, r d, r |

}



\score
{
<<
    \context Staff = oben \oben
    \context Staff = unten \unten
>>
}