Suppress command (\arpeggio) in music variable

[Joel C. Salomon]

I've got a bit of music that repeats -- except there's an arpeggio
that's only there the first time.  I've defined a music variable thus:

    barsSixToEight = {
    <<  \new Voice { \voiceOne
        d'8     cs      d       fs4->\arpeggio  e8      |
        d8      cs      b       cs4->           b8      |
    }   \new Voice { \voiceTwo
        fs8     g       fs      e4.\arpeggio            |
        fs4.                    gs                      |
    }
    >>                                                  |
        a8      a       gs      g       fs      e       |
    }

and I'm using it something like this:

    upperStaff =   \relative c' {
        a4 a a
        \barsSixToEight

        b4 b b
        % Somehow suppress \arpeggio here:
        \barsSixToEight
    }

> (The actual music is at 
> <https://github.com/jcsalomon/MutopiaProject/blob/03d5d92/ftp/CrookJ/PeterPan/PP01_Act_I_Opening_Music/PP01_Act_I_Opening_Music.ly>.)

As indicated, I do not want the arpeggio in the second repetition.

I've tried defining \arpeggioOnce,

    # (define arpeggioOnce arpeggio)

before defining \barsSixToEight, and then redefining \arpeggioOnce
within the music to something else (I defined \nill as an empty block)
but that did not work.

Is there a way to achieve what I'm trying to do?

--Joel Salomon