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I did some experimenting (PHP 4.3.2, Apache 2.0.46, Win2K) and found that if display_errors is off in php.ini, then calling ini_set('display_errors', '1') causes runtime errors to be displayed, but not parse errors.
Another option is to try changing the PHP error log file, if you don't have access to the existing one:
ini_set('log_errors', '1');
ini_set('error_log', '/your/path/php_errors.log');
If that works, at least you'll be able to read the errors in the log file.