[stavros]

Does this mean "remotes that speak the S3 protocol", or "remotes that are S3"? The former would require S3 supporting induced requests (so it POSTed the data somewhere), the latter would require a "copy" operation on S3. I don't know which one is supported.

[prirun]

Server side copy only works within the same service provider, not across service providers.

[seabrookmx]

Right because, how would that work otherwise?

Unless those providers natively supported this functionality (and they're incentivized to not) you'd _need_ an intermediary.