Hi Ian,
NO. It's true Dropbox uses Amazon S3 as its backend, but I don't know about the existance of any documentation on how it is implemented. I also doubt there is such a thing available.
I don't use Dropbox, but I'm pretty sure they have their own API to use it with external tools.
Official support for Dropbox in the Amazon S3 Interface is not planned. Maybe someone will implement it as a separate package.
Regards,
Peter