Converting ISO-8859-1 input document

We have a Unicode installation of Cache'. A client wants to send us documents that will be machine-read and loaded, automatically. They want to create the documents in ISO-8859-1 ("Latin-1"). We'd need to convert the text to UTF8 for our system. I saw the documentation on the $ZCONVERT function, but I didn't see this option. How should it be done?

Thanks!