Beaming across voices and staffs

[Niels]

See the following example:

\version "2.20.0"
\score {
  \new PianoStaff
  <<
    \new Staff {\clef G c''8 r}
    \new Staff {\clef F r8 c}
  >>
}

Is it possible to have a beam between the c'' and the c when they are 
different voices and different staves?
Of course the problem can be solved using changing staff, but then the 
rest in the upper staff is not shown:

\score {
  \new PianoStaff
  <<
    \new Staff = "up" {\clef G c''8[ \change Staff = "low" c8]}
    \new Staff = "low" {\clef F r8 s8}
  >>
}