Macro preprocessor

Hello everyone,

I am very new to SableCC, so please bear with me.  I would like to
implement an Erlang parser, and I've written the main grammar.
However, Erlang supports preprocessing.  For example, macros can be
defined and applied as:

  -define(MACRO, "abc").
  f() -> ?MACRO.

I am trying to understand how to create a preprocessor that integrates
with SableCC.  I've looked at the Java 1.5 unicode preprocessor, but
that is much simpler than what I need -- it simply replaces escaped
tokens as they occur.

I've thought of writing a preprocessor grammar, parsing the text once,
modifying the AST, outputting back to a string, and finally reparsing
with the main grammar.  But my gut feel is that that's a poor
approach, especially with the need to output an intermediate string.

Is there a standard way of doing this, or an example of this anywhere?
Is there a simple way to chain a preprocessor and parser together in
SableCC?

Thanks for your help!

Jonathan