io.Pipe与WriteAtBuffer

I would like to download and upload a file to aws s3 using streaming. I wished to use io.Pipe but I can't because the downloader struct

https://docs.aws.amazon.com/sdk-for-go/api/service/s3/s3manager/#Downloader.Download

uses a "WriterAt" interface. and io.Pipe provides an io.Writer I didnt succeed using the regular GetObject because it creates it downloads the object and doesn't receive a writer any solution for that?

thanks.