Though I have not used this product on a Mac, nor in this particular way, it should work.
there is a product called Syncovery which will backup selected files to "FTP, SSH, HTTP, WebDAV, Amazon S3, Google Drive, Microsoft Azure, SugarSync, box.net and many other cloud storage providers". We use it successfully to copy backups from a local server to our Amazon S3 account.
I would imagine that you could tell Syncovery what source to use and it would back up your time capsule to Amazon S3 (or other). As I have not used this specific app for this specific function I would recommend asking their tech support to verify if this is something they support.
Note I have no financial interest in this company, just a satisfied user of their (PC) product.