Do i really need to hack core to install Amazon S3 Module?
I think you should give a try to S3FS module


  S3 File System (s3fs) provides an additional file system to your
  drupal site, which stores files in Amazon's Simple Storage Service
  (S3) or any other S3-compatible storage service. You can set your site
  to use S3 File System as the default, or use it only for individual
  fields. This functionality is designed for sites which are
  load-balanced across multiple servers, as the mechanism used by
  Drupal's default file systems is not viable under such a
  configuration.