How to create ftp user with access to subfolder in the another user's home directory?

Hello. I have some user, for example, “example” :) And his home directory is /var/www/example/, where are sites folders (/var/www/example/example.com). For ftp access I use this user’s login “example” and his password. But. I need to create another one ftp user, with access to the folder /var/www/example/example.com/subfolder and only to this folder. I can’t create a unix user with such home directory. Is there a way to resolve this problem?