[rmc]

Using S3 torrents wouldn't help you seed, since you'd have to use the same tracker (original) as everyone else.

[zmitri]

Couldn't you just add the tracker url from the s3 torrent to the torrent file you generate?

[rmc]

Sure, but you then need to get everyone else downloading the (original) torrent to download and use your new torrent. The new amazon torrent might split the file into differently sized chunks compared to the original. In short, you'd need to get all original downloads/uploaded to use your new torrent.