I've not used Amazon's S3 services, but I'm getting more interested in them, it looks like something I'll have to get to grips with soon.
For now though, can you not just use rsync to move files to the host? If so, a cronjob to sync the two folders could be setup, that should sort it out. It will all depend on how large your backups are, how much bandwidth you have and how often you backup
