For my clients with Premium hosting plans there is a great option to get extended storage. With LargeFS you need an Amazon S3 account, and you would send us your account details to setup your LargeFS account. Once the files are over sixty days old, the system will move them over to your Amazon S3 account. You can create a new bucket for each domain if you want.
You can sign up for a free S3 account with 5GB of storage.
Once LargeFS is setup our system will tell the site to retrieve the files from Amazon S3 when these are called.
They have a blog article that goes into depth about the LargeFS system.