Set up an FTP user for him using the console:
Setting up a user
Information about users
If you go Here and add an FTP only user, you can give him a directory that is safe for him to put files into. It does NOT have to be a published directory.
Wholly - IS NOT MY PROMO CODE. Even worse, I don't get any credit for it. Use WhollyMindless for full credit. I'm really disappointed in someone.