Spacing broken tie away from key signature

[Nick Payne]

When a tie is broken across staves, the second part of the tie defaults 
to starting right at the key signature. How can I move it slightly away? 
Setting extra-spacing-width for the KeySignature moves the first note 
further away but doesn't move the starting point of the broken tie. I 
also played around with the various space-alist values for KeySignature 
without being able to move the tie. When I look at commercial scores I 
have, there is usually about one staff unit space between the key 
signature and broken tie in this situation

version "2.13.58"

notes = \relative c'' {
    c1 ~ c ~ c ~ c ~ c ~ c ~ c ~ c ~ c ~ c ~ c ~ c ~ c ~ c ~ c ~ c ~ c 
~ c ~ c
}

\score {
<<
    \new Staff {
        \key g \major
        \notes
    }
>>
    \layout {
        \context {
            \Staff
                \override KeySignature #'extra-spacing-width = #'(0 . 4)
        }
    }
}

Nick