Externalizing preamble material and using lilypond-book

lilypond-book processes this minimal LaTeX file just fine.

   \documentclass[10pt]{article}
   \begin{document}
   Hello!
   \end{document}

But when we externalize the one-line preamble to a separate file, lilypond-book grumbles.

   \include{test-preamble}
   \begin{document}
   Hello!
   \end{document}

With the contents of test-preamble.tex as \documentclass[10pt]{article}.

$ lilypond-book --pdf --output=out test.tex
   lilypond-book (GNU LilyPond) 2.11.43
   Reading test.tex...
   Running latex...This is pdfTeXk, Version 3.141592-1.40.3 (Web2C 7.5.6)
    %&-line parsing enabled.
   entering extended mode
   (/tmp/tmpUlfqXl.tex
   LaTeX2e <2005/12/01>
   Babel  ...

   \@input{test-preamble.aux}
   No file test-preamble.tex.
   No file tmpUlfqXl.aux.

   ! LaTeX Error: The font size command \normalsize is not defined:
               there is probably something wrong with the class file.

   See the LaTeX manual or LaTeX Companion for explanation.
   Type  H   for immediate help.
    ...                                             
                                                 
   l.5 \begin{document}
                   
   textwidth=8191.99998pt
   columnsep=0.0pt
   (./tmpUlfqXl.aux) )
   (see the transcript file for additional information)
   No pages of output.
   Transcript written on tmpUlfqXl.log.
   command failed: latex /tmp/tmpUlfqXl.tex
   Child returned 1

So does lilypond-book know how to process LaTeX \includes? Or is this a known limitation for which the workaround is not to externalize when using lilypond-book?