My VPS is set to disable the following functions:
root@vps [~]# grep disable_functions /usr/local/lib/php.ini
disable_functions = dl, exec, shell_exec, system, passthru, popen, pclose, proc_open, proc_nice, proc_terminate, proc_get_status, proc_close, pfsockopen, leak, apache_child_terminate, posix_kill, posix_mkfifo, posix_setpgid, posix_setsid, posix_setuid
PHP has enough potentially destructible functions that your list might be too big to grep for. For example, PHP has chmod and chown, which could be used to simply deactivate a website.
EDIT: Perhaps you may want to build a bash script that searches for a file for an array of functions grouped by danger (functions that are bad, functions that are worse, functions that should never be used), and then calculate the relativity of danger that the file imposes into a percentage. Then output this to a tree of the directory with the percentages tagged next to each file, if greater than a threshold of say, 30% danger.
