On my local setup I have a load of different CakePHP websites. I\'m using a Mac so the folder structure is something like ~/Users/cameron/Sites/sample-website a
If you have access to your php.ini, you can add the path to Cake core there. Doing it this way means you don't have to change webroot/index.php at all. Example in php.ini:
include_path = ".:/usr/local/lib/php:/home/something/phpinc/cakephp2/lib"
According to the CakePHP 2.x docs, this is the recommended way to share the Cake core (assuming you have access to your php.ini).