Considering your support threads here , here and here, This Amazon s3 and cloudfront plugin have got you covered,it will solve your issue.
Once installed, go to the plugin settings page, switch on the path option and you would notice an input field will immediately appear underneath, by default , the value would be something like this “wp-content/uploads” , now edit that input field and append your desired folder name like this ” bar/wp-content/uploads” and save your options.Then your url should come something like this.
https://s3?us?west?1.amazonaws.com/bucket-name/bar/wp-content/uploads/photo.jpg
However you can further extend your folder structure by enabling the year/month option. So your url could appear something like this
https://s3?us?west?1.amazonaws.com/bucket-name/bar/wp-content/uploads/2015/03/photo.jpg
