Avoid collision between fingering and other voice [with edition-engraver]

[Urs Liska]

Attached you see how a fingering collides with a note in another voice.

Is there another way to fix this besides \tweak-ing the fingering (and 
what would be the best property for this case)? I have to set the 
fingeringOrientations like this due to the context.

And: if I have to use a \tweak, what would be the way to apply it with 
the edition-engraver?

Thanks
Urs

\version "2.19.80"

\new Staff {
  <<
    {
      \voiceOne
      b'-1
    }
    \new Voice {
      \voiceTwo
      \once \override Fingering.color = #red
      \set fingeringOrientations = #'(down left)
      <e'-4 a'-3>
    }
  >>
}

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