In your case, maybe putting the configuration data in the DATA section could help.

If you store your "sane" configuration data in the DATA section and initialize your stuff from there, you can after that go looking if the user specified another configuration file and read that in in the same manner you did read in your DATA section. Thus you have both, a single file that works and the option to have a configuration file.

For an example on how to use the DATA section, go here (the sourcecode version of the node)