How to get the permalink of a page when loading my plugin

I’m implementing a web widget and for this reason I’d like my script to respond to the request as soon as possible, to avoid loading unnecessary thing.
I’ve found out that calling get_permalink( $page_id ) before the init phase return this error:

[19-Sep-2012 12:10:12 UTC] PHP Fatal error: Call to a member function get_page_permastruct() on a non-object in ...\wp-includes\link-template.php on line 276

I was wondering is there a way in which i can retrieve the permalink of the page without waiting for the init phase?

setup_theme is the earliest action you can call get_permalink() on. the rewrite class gets instantiated after plugins_loaded and before setup_theme in wp-settings.php, which is the object the error refers to. get_page_permastruct() is a method of the rewrite class.