This value is generally set in the httpd.conf (server) file, which is generally not accessible to users on shared hosting packages. So, here are a few ways to get around this.
In a ‘.htaccess’ file, stored in web root:
php_value register_globals on
or in a ‘php.ini’ file, also stored in the web root:
register_globals = on
More details on this and other override settings can be found in this excellent article: http://www.sitepoint.com/blogs/2010/03/04/how-to-override-php-configuration-settings/