Proftpd and mounting with bind option
There’s only one good way to export resources to chrooted enviroment - using mounting directores to several locations in the filesysem. If you want to have an exact duplicate of the /var/ftp/common directory available for user alex at his /home/alex/common, use one these commands:
mount -o bind /var/ftp/common /home/alex/common
mount -o bind /var/ftp/common /home/alex/common
To keep directories mounted permanently you need to add them into /etc/fstab ( or /etc/vfstab for Solaris ).