Domain Security Restrictions

Our company is currently running a server which is responsible for hosting numerous domains. As a web development firm, traditionally our server has been set up so that only our developers have access to run scripts on it. Recently some of our clients have been looking for FTP access to their sites, mostly static, so that they can make additions directly, and as such we are looking for a way to securely offer them this service. Essentially, I am looking for a way to do one or all of the following: 1) Enable safe mode on a domain by domain basis. 2) Disable the use of specific functions on a domain by domain basis. 3) Disable php entirely on a domain by domain basis. Any help or advice with any of the above would be greatly appreciated. Nick Oostveen