The fastest way would be:
1) Copy all wordpress files from the original folder to the folder that site2.com is assigned to.
2) Create a new database for your copied site in the "MySQL Databases" icon in cPanel (at this point you may as well create a new username and assign it with full privileges as well).
3) Then you can use the "Synchronize" tool in phpMyAdmin to copy the content from the old database to the new one (phpMyAdmin > More > Synchronize).
4) Update the wp_options.siteurl and wp_options.home values in your new database to reflect the new domain name.
5) Update the wp-config.php file for the new site to make sure it's connecting to the new database and not the old one.
At that point, you should be good to go. Bluehost's support team should be able to help with any snags along the way.