You can leave Bruce a question regarding his tutorial there, but you can put the functions he gives in a must-use plugin. http://codex.wordpress.org/Must_Use_Plugins
Basically put the PHP file with your code in the the /wp-content/mu-plugins/ directory and it’ll be loaded automatically by WordPress.
You can use the vars directly in your Membership Options Page, though. See the documentation here: [hilite path]Dashboard -› s2Member® -› API / Scripting -› Membership Options Page Variables (MOP Vars)[/hilite]
ou will need a PHP execution plugin, there are several available: http://wordpress.org/plugins/search.php?q=php+execution