\version "2.19.25"

\score {
  \new PianoStaff \with { \consists #Span_stem_engraver }
  <<
    \new Staff
    <<
      \repeat tremolo 4 {
        \once\override NoteColumn.force-hshift = #-1
        a'16 bes'16
      }
      \\
      {
        \voiceFour \crossStaff {
          % With this override, the span stem is correct,
          % but the first and second voices collide…
          %\once\override NoteColumn.ignore-collision = ##t
          <g' e'>4.
        }
      }
    >>
    \new Staff
    <<
      \clef bass
      { \voiceFour cis'4. }
      \\
      { \voiceTwo a,2 }
    >>
  >>
}