PHP 4.3.0 safe_mode

I am running Apache 1.3.27 with PHP loaded as a module and I have several sites on the server running. I want to enable safe_mode so that PHP can be more secure on the server so one user can't read another users files. However I notice that with safe_mode enabled it denies readfile function, but the include and require functions are allowed to read the file. Is there a way to get it so that any include or require statements will have the UID checked like readfile does? Any help would greatly be appreciated. Thanks Devin Atencio