\version "2.19.28"
crossStaff =
#(define-music-function (notes) (ly:music?)
   (_i "Create cross-staff stems")
   #{
     \temporary \override Stem.cross-staff = #cross-staff-connect
     \temporary \override Flag.style = #'no-flag
     \temporary \override TupletBracket.stencil = ##f
     \temporary \override TupletNumber.stencil = ##f
     \temporary \override Beam.stencil = ##f
     #notes
     \revert Stem.cross-staff
     \revert Flag.style
     \revert TupletBracket.stencil
     \revert TupletNumber.stencil
     \revert Beam.stencil
   #})
\score {
  \new PianoStaff <<
    \new Staff { c'8 d' \tuplet 3/2 {e' f' g'}}
    \new Staff {\clef bass \crossStaff{\stemUp c8 d \tuplet 3/2 {e f g}}}
  >>
  \layout{
    \context {
      \PianoStaff
      \consists #Span_stem_engraver
    }
  }
}