Restrict 'cPanel FTP' user from becoming Unix user

[bodomic]

I was questioned by my client who had become very concerned after his own client installed myftp into his ftp folder.
The problem is the following:
Let's say I have created account main_user for my main user in WHM.
He goes to his cPanel and creates FTP user for his client his_client@myhost.com.

Then, his_client copies myftp folder to /home/main_user/his_client/myftp and sets "../.." as home directory for myftp web interface.

That's very, very bad... /home/main_user/his_client/myftp and its contents are owned by main_user, so his_client can go to http://main_user.com/his_client and have a full access to /home/main_user indeed...

I've edited config of myftp and denied anyone but root edit it, so it is fixed by now but I'm curious - is there a way of restricting user-behind-user from doing such terrible things? And of course it would be great if I could restrict this automatically for any new FTP user.

Thanks

[bodomic]

can anyone help?