Using ESCA key to login by --ssh argument

It seems that we can not use wp-cli to remote with ECSA key?

If we want to log in some instance like AWS ec2 or instance in Google Computer Engine, It is necessary to create a SSH key first. And then login by command like this:
ssh -i /path/to/key.pem user@ipaddress -p port

but a little pity about using --ssh on wp-cli is that, It seems like we cannot allocate the path to key file for login using.