\version "2.18.2"

\parallelMusic #'(voiceA voiceB) {
  \time 2/4
  s2	|
  g,32 [ d' \change Staff = up d' gis a c d g ] \change Staff = down g,,4 |
}

\new PianoStaff <<
  \new Staff = up \relative c' { \voiceA  }
  \new Staff = down \relative c' {
    \clef bass 
    \voiceB
  }
>>