Reduce width of single measure

[Nick Payne]

How can I reduce the width of a single measure? i.e. in the final bar 
below containing the chord of whole notes, I want the width of the 
measure to be just wide enough to contain the chord.

\version "2.15.20"
\language "english"

\score {
<<
    \new Staff \relative c' {
        \override Staff.TimeSignature #'stencil = ##f
        \set Score.markFormatter = #format-mark-numbers
        \clef "treble_8"
        \bar "|:"
        \repeat volta 2 {
            \mark #83
<<
            {
                c,16 g' c g <e e'> g c g c, g' c g <e e'> g c g |
                b, g' d' g, <d f'> g d' g, g, g' d' g, <b, f''> g' d' g, |
            }
            \\
            {
                c,4 e c e |
                b d g, b |
            }
>>
        }
<e' c g e c>1 |
        \bar "|."
    }
>>
    \layout { }
}