vertically center rests in polyphonic voices

[Jin Choi]

I’m transcribing some piano music where it is helpful to use \voiceOne and 
\voiceTwo for some extended polyphonic sections. When I come across shared 
rests, I’ve been putting in rests in one voice and invisible rests in the other 
voice. But rests in voices are vertically offset from the center depending on 
which voice is in use:

\version "2.24.1"

upper = \relative c'' {
  \new Voice {
    \voiceOne c4 r4 c4 r4
  }
  \new Voice {
    \voiceTwo c4 r4 c4 r4
  }
}
\new Staff = "upper" \upper


I can fix that by exiting the voice context and going to \oneVoice for the 
rests, but is there an easier way just to have the rest vertically centered?