Creating Alternate RSS Feed

My normal RSS preferences are set to do excerpt only.

I need to have a special, secret RSS feed that gives out full text for certain partners of mine.

I found these instructions which seem to be perfect:
http://wordpress.stackexchange.com/questions/22849/how-to-create-additional-full-text-rss-feeds/

However, naturally, something is wrong! Can anyone decifer exactly what is supposed to go into the “functions.php” file to make this work? Following the example just yields a blank page for me…

Any other clever way to do this?