This simple plugin will allow you to put the contents of a custom field where you put the shortcode [putthemeta key=""] where key is the key of the requested custom field. Great (and created) for Google Adsense Code
Please visit
https://bitbucket.org/enethrie/wp-put-the-meta/ for more information and wiki.
To install this plugin just copy the .php file to your wp-content/plugins folder, or use WordPress Dashboard to install this plugin by searching for it.