When overwriting a value for a single site using php.ini, I highly suggest copying the root level php.ini (located at /usr/local/lib/php.ini for most suPHP enabled Linux servers) to the directory in question, changing the one value needed, then chowning the file to the user, rather than making your own custom php.ini with one line of the value that is being overwritten. The reasoning behind this is that when you make an empy php.ini with just the one directive, many issues including but not limiting to the following arise:

• safe_mode defaults to On instead of Off
• pdo or any other includes such as zend or ioncube are no longer loaded
• disable_functions line is nullified

Anyways, just a tip for anyone out there using such changes! Let me know if you have any questions about this in the comments!