SyncBackPro V6 and newer versions can backup and sync with Amazon S3 (and also Microsoft Azure and Google Storage) directly. SyncBackPro V7 and newer versions can backup and sync with Dropbox, Google Drive, OneDrive, Office 365, Amazon Drive, SugarSync and Box. SyncBackPro V8 can also backup and sync with OpenStack and Backblaze B2. SyncBackPro V9 supports backup and sync with OVH, Egnyte, hubiC and WebDAV. It can also retrieve objects stored in Amazon Glacier via S3.

For SyncBackPro V5, SyncBackSE and SyncBackFree you would first need to install and configure a 3rd party utility that maps your S3 storage to a drive letter. Examples are TntDrive and WebDrive:

Note that it is unlikely you can use such mapped drive letter/s and also Schedule the profiles, because mapped drive letters are typically not re-created by Windows (or 3rd-party software) when logging on a batch job (which is how Scheduled Tasks work) - as per paragraph-2 here.