Ways to achieve de-duplicated file storage within Amazon S3?

Question

I am wondering the best way to achieve de-duplicated (single instance storage) file storage within Amazon S3. For example, if I have 3 identical files, I would like to only store the file once. Is there a library, api, or program out there to help implement this? Is this functionality present in S3 natively? Perhaps something that checks the file hash, etc.

I'm wondering what approaches people have use to accomplish this.