How do I force a group on directories created by ftpd?

I have an FTP root direcotory at /Volumes/HD1/FTP/. The permissions for FTP are owner: "admin"(R/W/X), group: "ftp"(none), everyone(none). The server does not have anonymous access. Each ftp user has a home directory inside /Volumes/HD1/FTP/ The ftp users are NOT members of the group ftp. That group is for other users that have privileges to read this directory over afp:// The problem is that when ftp users create sub-directories in their home folder the directories are created with the these permissions: owner:"ftp-user1"(R/W/X), group: "ftp"(R/X) and everyone(R/X). How can I give members of group ftp write access to these directories?