Setting up Pure-FTPd with admin/user permissions for same directory

I need to set up 2 Pure-FTPd accounts - ftpuser and ftpadmin. Both will have access to a directory that contains 2 subdirectories - upload and downlaod. The permissions criteria needs to be as follows:

• ftpuser can upload to /upload but cannot view the contents (blind drop).
• ftpuser can download from /download but cannot write to it.
• ftpadmin has full read/write permissions to both, including file deletion

Currently, the first two are not a problem - disabling /upload read access and /download write access for ftpuser did the job. The problem is that when a file is uploaded by ftpuser, it's permissions are set to 644, meaning that user ftpadmin can only read it (note that all FTP directories are chown'd to ftpuser:ftpadmin). How can I give ftpadmin the power he so rightfully deserves?

From serverfault modulaaron

• Starting the process with a different umask (-U) flag set will solve the permissions issue. For example:

  /usr/sbin/pure-ftpd -U 113:002 &

  Note that each umask number is subtracted from 7 to get the final permissions:

  113:002 results in 664 for files and 775 for directories.

  From modulaaron

• Just set the sgid bit on the top dir, since group is already set correctly you're done.

  From CarpeNoctem