How to add data to Drupal.settings without drupal_add_js
Maybe I am missing a point to the question, but you should be able to do

scripts[] = path/to/your/script.js


in the .info file of your theme.  And within the script file something like

(function ($) {
$(document).ready(function () {
    Drupal.settings.yoursetting = {};
    Drupal.settings.yoursetting.property = some_value;
});
})(jQuery);


or use the Drupal.behaviors convention.