An easy way to surface XLS, CSV, RTF (DOC), PDF etc files to customers is by installing a web server on your UNIX machine, e.g. Apache.
Then you can send customers URL links to SAS output files, or create custom HTML pages that are built dynamically to contain links to standard output files.
FTP and other such methods usually need a login at both ends, with hardcoded passwords.
In terms of the big picture, you may want to ask customers why they need to manipulate SAS data in Excel. If you figure out a way to change these habits, let us all know please.