Change staff and cross staff

[Knute Snortum]

I have a tricky measure in the Chopin Mazurka I'm working on.  The
notes need to be on the lower staff (from the right hand) and the last
chord is cross staff.  I'd like to be able to do something like
this...

%%% Start
\version "2.20.0"

staffUp   = \change Staff = "upper"
staffDown = \change Staff = "lower"

\relative c, {
  \staffDown <gs b>8[ r16 <b \staffUp \crossStaff e>
}
%%% End

..but of course that doesn't work.  I tried something with two voices
in the left hand, but ran into problems.  I've attached a screenshot
of the measure.

--
Knute Snortum

chopin-o6-3-measure-21.png
Description: PNG image