s3 sync: ability to compare based on filename alone

I was going to move from using s3cmd to the official was-cli, however there's one feature that appears to be missing that I use. The `--skip-existing` option.
During a sync operation, this would only copy a file if there wasn't a target file of the same name (regardless of size or md5 comparison).

Is there any comparable method within the existing toolset or is this a feature request?