cross staff melody

[Helge Kruse]

Hello,

I have a voice in the lower staff, that is so high, that it should be noted
in the upper staff, but logically it belongs to "lower". I tried to edit
this with staff change, but the "upper" staff is already full and the six
16th notes are moved to the next measure. 

How can I get these six 16th (gfgfgf) to the first measure? I would prefer
to keep the <es es>2. in the upper staff, but probably this is not possible?

Regards,
Helge

\version "2.7.39"
\include "deutsch.ly"

upper = \relative c'' 
 {
        \clef treble
        \key b \major
        \time 6/8

        <es, es'>2. |
}

lower = \relative c
{
        \clef bass
        \key b \major
        \time 6/8

        << { r8 f16 ( g ) f8 } \\ c2. >>
        
        \change Staff = "upper"
                g'''16 ( f ) g, f 
        \change Staff = "lower" 
                g, f |
}

\score 
{
        \context PianoStaff <<
           \set PianoStaff.instrument = "HARPE  "
           \context Staff = upper \upper
           \context Staff = lower \lower
        >>
        \layout { }
}