Proftpd upload and hidden files

[slam_head]

I want to have anonymous upload availble but i want to stop people from leave hidden files that start with either a space or a dot. Any ideas? Here's my upload directive:

# Limit WRITE everywhere in the anonymous chroot
<Limit WRITE>
DenyAll
</Limit>

<Directory upload/*>
<Limit WRITE>
AllowALL
</Limit>
</Directory>