Yes, you can disable any arbitrary internal function in PHP using disable_functions[1] directive in php.ini

[1] http://php.net/manual/en/ini.core.php#ini.disable-functions

Edit: Also, as noted below, this wouldn't prevent this or many other similar hacks as you need write access to the PHP script to put the eval in in the first place, so you could just write other code in there directly (and pull in extra scripts to execute by writing to disk etc. if necessary). Eval is typically dangerous, in its own right, when it is used by the legitimate developer who then allows unchecked code to be passed to it.