Actually there is no way to use symbolic links in FTP. A workaround is to mount the folder with the bind option. For example, i have a jailed FTP account and i want to allow it to access the /tmp/eureka folder.
1. Create the mount point folder in the user home directory.
2. Mount the /tmp/eureka folder with the bind option.
mount --bind /tmp/eureka /home/<username>/eureka
Reference: vsFTPd and Symbolic Links