HaraKiri in PianoStaff

[John Galbraith]

Is there a way to make the bass staff of a PianoStaff disappear when
there is nothing in it?  This seems like what I want, but it doesn't work:

\context PianoStaff \notes <
   \context Staff = "up" <
     \property Score.skipBars = ##t
     \clef treble
     \global
     \organ
     >
   \context HaraKiriStaff = "down" <
     \property Score.skipBars = ##t
     \clef bass
     \global
     \organbass
     >
>

I get a message 
"warning: can't find or create `HaraKiriStaff' called `down'"
in the interpretation phase.  Then I get three staves in the output, and 
the order is all out of whack.

I also tried adding
\translator { \HaraKiriStaffContext }
to my paper definition, but this wipes out both staves when both staves
are empty, which doesn't look good for orchestral parts. 

Thanks for any advice,
       John