Org-Mode: Exclude specific code line from html export

Question

I'm writing a Lilypond typesetting tutorial in Org to be published on a web page. I would like to exclude the line with set-default-paper-size from html export, cause it doesn't belong to the tutorial but is needed to shrink the size of the resulting png. How could this be done?

#+begin_src lilypond :file c-major.png :exports both
#(set-default-paper-size "a9" 'landscape) % How to exclude this line from export???

{ c d e f g a b c }
#+end_src
#+results:
[[file:c-major.png]]

An alternative would be if babel could invoke lilypond with the -e option when evaluating the code block. Any other ideas how to hide specific code lines are appreciated as well.

EDIT: The following solution works fine for a single code block:

#+begin_src lilypond :file c-major.png :exports both :prologue "#(set-default-paper-size \"a8landscape\")"
{ c d e f g a b c }
#+end_src

All I have to do is to escape the double quotes. Now I try the same for a default setting in .emacs:

(add-to-list 'org-babel-default-header-args:lilypond
             '((:prologue . "#(set-default-paper-size \"a8landscape\")")))

Then the following error message is thrown:

org-babel-exp process lilypond at line 38...
Wrong type argument: stringp, (:prologue . "#(set-default-paper-size \"a8landscape\")")

This is the full backtrace:

Debugger entered--Lisp error: (void-function stringp\?)
  (stringp\? "#(set-default-paper-size \"a8landscape\")")
  eval((stringp\? "#(set-default-paper-size \"a8landscape\")") nil)
  eval-last-sexp-1(nil)
  eval-last-sexp(nil)
  call-interactively(eval-last-sexp nil nil)
  command-execute(eval-last-sexp)

Answer 1

Take a look at the prologue header argument for Babel source blocks. You can use it to prepend some text to a code block prior to execution, and, like any other header argument, it isn't included in HTML export.

For example:

#+NAME: prologue-example.sh
#+BEGIN_SRC sh :prologue "echo yep; exit 0"
echo "nope"
#+END_SRC

#+RESULTS: prologue-example.sh
: yep