The only OS where I have ever seen such FILE statement syntax is z/OS (MVS) where you have a pre-defined JCL DD statement pointing to a PDS or PDSE library, or you have a SAS-defined FILENAME pointing to the library and the member name is placed inside the parentheses. If you have a predefined FILENAME (or an external JCL DD on MVS) and you do not want a PDS (or if it is not an MVS environment), you specify the SAS FILENAME or the FILE statement with the complete file name defined in quotes. And when using ODS, you would specify FILE= parameter.
Now back to the question. The environment I am working in assigns the library where the text files are to be placed (which of course changes between Development and Production environments) but not the path for this library. Sure I would change that if I could, and I may have to. But it would be more consistant with the structure I am working in to be able to reference the file by fileref and filename rather than fully qualified name.
Don't know if this is silver bullet but it seems obvious.
Since the parenthesized file name syntax does not work, don’t use it. You have the FILEREF to the aggregate location so just make a new FILEREF using the information you have plus the file you want to create.