Ottava collision with bar line

[David Bellows]

Hello all,

In the example below when you get to the second measure the ottava
symbol "8va" collides with the bar line. I know that typically these
symbols will be above the upper staff or below the lower staff but not
in the middle like this but for this score it is necessary. For the
time being I've replaced the "8va"s with "8"s and it works fine (no
collisions) but I'd like to learn how to fix this anyway by nudging
the "8va" symbol over.

\version "2.17.25"
\language "english"
upper = { a'4 a' a' a' a' a' a' a' }
lower ={ cs''1 \ottava #1 < a'' cs''' g''' > \ottava #0 }
\score {
\new PianoStaff<<
\new Staff="upper" \upper
\new Staff="lower" \lower
>> }

Thanks,
Dave Bellows