Write me a script using AWS PHP SDK for Multipart Upload

Every 6 hours, a backup of our site takes place and is stored on our server in a folder outside of public_html. I would like to be able to run a cron job that uploads this file to our Amazon S3 account. I would use the regular S3 upload code but the file is over the max file size limit so it needs to be done with the multipart uploader. I have installed the SDK on our server so all I need you to do is write the script that takes the file and uploads it to our S3 account in a specific bucket and folder (I'll give you these details later). I need to be able to set up a cron to run this script multiple times per day so it's important it also doesn't slow down the functioning of our site/database.