Disable scripting / set home directory of user

I have a subdomain that is used by several people who all log in as the same user (through FTP only).

For safety, I’d like to disable PHP and any other form of server-side scripting for this subdomain. However, the only way I can see how this could be done would be by setting it in a .htacess file.

Unfortunately, the way the system works now, the user I’ve set up controls his entire home directory. And because my main user has no access to the new user’s home directory, I can only create files that are owned (and deletable) by the new user.

Is there a way to give a user a new home directory - perhaps even a subdirectory of my main user’s home directory? Or if that’s not possible, at least switch off scripting permanently?