Yes, you can, you can pipe tar to the AWS CLI to upload a stream, like "tar -c ./myfiles | aws s3 cp - s3://my-bucket/myobject".

For very large uploads you must also specify a chunksize using "multipart_chunksize" such that the upload will require 10,000 chunks or fewer (the CLI can't do this for you because it doesn't know the size of your stream up front).