precisely controlling with width of an example

[Kevin Patrick Barry]

Dear LilyPond users,

I am doing musical examples for a book, and the publisher requires a precise width of 4inches.  Is there any way to accomplish this in LilyPond?  I can set the line-width or the paper-width to 4 inches, but in both cases LilyPond will produce slightly wider examples to include the system start brace, bar numbers, or instrument names.  In printed music these things normally stray into the left margin, but I don't have that option for the book.  For now I have to manually add a margin of the right size depending on what kind of system delimiter there is, and how many digits there are in the bar number, which seems clunky.  Does lilypond-book have some clever way of avoiding this problem? I know it automatically detects the width of the textblock.

Here is a short example of what I am trying.  Instead of a 4-inch image I am getting 4.08 (adding a left-margin of .08 inches solves the problem).

\version "2.18.0"

#(ly:set-option 'backend 'eps)
#(ly:set-option 'aux-files #f)

\paper {
  tagline = ##f
  paper-width = 4\in
  left-margin = 0
  right-margin = 0
}

\score {
  \new PianoStaff <<
    \new Staff { c'1 }
    \new Staff { c'1 }
  >>
  \layout {
    indent = 0
    ragged-right = ##f
  }
}