Between-staff beam wrong direction

[Mark Witmer]

Hi,

I'm trying to typeset something like the following example:

\version "2.17.10"

\new PianoStaff <<
  \new Staff = "up" \relative c'' { 
    r4
    \change Staff = "down" \stemUp c16 
    \change Staff = "up" \stemDown <a e> c, a } 
  \new Staff = "down" \relative c'' { r4 s }
>>

The result is attached. Is there a way to force LilyPond to add enough space between staves so that the beam moves up from left to right? 

I've tried to modify StaffGroup.staff-staff-spacing.stretchability and the length of the stems connected to the beam, but the first causes unwanted space between staves elsewhere in my score, and the second simply increases the downward slope of the beam.

Thanks,

Mark Witmer

beam.preview.png
Description: PNG image