seperated stems

[Helge Kruse]

Hello,

I want to write some chords, played with both hands, in one staff. To 
indicate that it's played with two hands, I want to write some of the notes 
with stem and beam up and some other down. The excerpt below combines both 
chord with one stem and one beam.
How do I get one beam above and one beam below?

\version "2.10.4"
\include "deutsch.ly"
\score {
\relative c'' {
 \clef treble
 \key a \minor
 | \repeat "unfold" 8 { << <c, e a>8 <c' e a> >> }
}
}

Best regards, Helge