Merging stems with three voices on one staff

[Morten Lemvigh]

I have three parallel voices on one staff. The stems of two of the 
voices point in opposite directions and the last one is shifted. Which 
looks a bit cluttered with respect to both stems and beams.

Is the some way to merge the stem and beam of the middle note with one 
of the other voices?

I've attached a small example.

Regards,
Morten

\version "2.10.33"

\header {
  title = "Test"
}

global = {
  \clef "G_8"
  \key c \major
  \time 4/4
  \tempo 4=60
}

melody = \relative a {
  a8 g b a g b
}

tmelody = {\transpose a c' \melody}
tglobal = {\transpose a c' \global}

musik = {
  \context StaffGroup <<        
        \context Staff = tenor <<
          \tglobal
          \context Voice = "ftenor" {\voiceOne \tmelody} \\
          \context Voice = "atenor" {\voiceThree {\transpose c g, \tmelody}} \\
          \context Voice = "ttenor" {\voiceTwo {\transpose c c, \tmelody}}
    >>  
  >>
}

\score {
  \musik
  \layout {}
}