Ok, so looking over the docs at proftpd (I'm still assuming that's the FTP server you are using
) it looks like you could set it up on a per directory basis on the server side. If this is a public folder you probably don't want to do this. If this is public, you could setup a private directory where your user ftp's into, make it have the chmod 777/umask 000 and then have a cron setup to move the files (every 5 minutes or so) in /path/to/private to /path/to/public after chmodding them 555 or something more restrictive. Here's the directory syntax I'd try in the proftpd.conf file (make sure you are doing this outside of your <Anonymous> block):
Then restart proftpd either by sending the HUP to your inetd pid or for standalone just restarting proftpd:
Short of that working, you could setup a cron to chmod your files, but that would be taxing your system if you had it running every minute. Another option is to setup a global umask 000 and then set limits in every users profile (if that's even feasible) to restrict that.
If none of that works, post back and I'll do some more looking