how can i reference $_SERVER['DOCUMENT_ROOT'] in a .htaccess file?

Question

How can i reference the document root from within an htaccess file?

ie:

i currently have

php_value auto_prepend_file  C:/wamp/www/hf_latest_desktop/prepend.php

but i would like

php_value auto_prepend_file  **AUTO_DOC_ROOT**prepend.php

where '**AUTO_DOC_ROOT**' the root path

Answer 1

You won't need to have an absolute path if the file in question is in PHP's include_path

Answer 2

You cannot. Apache configuration files do not support this.