Is there a way to pass additonal php.ini settings to a drush command?
In the Drush README file, in the section titled "CONFIGURING PHP.INI", you will find instructions on how to set php configuration variables without modifying the drush script:

export PHP_INI='/path/to/php.ini'
export DRUSH_INI='/path/to/drush.ini'
export PHP_OPTIONS='-d memory_limit="128M"'


The first option replaces the entire php.ini file with one of your choosing.  The second option allows you to specify an ini file that is merged in with the standard php-cli ini file.  The last option allows you to specify commandline options to set configuration values.  Note that the second option effectively works the same way as the third option -- all of the settings are converted to commandline options.  See the php documentation for more information on php commandline options.

If you want to do this for just one call:

alias specialdrush='/usr/bin/env PHP_OPTIONS="-f /path/to/my/php.ini" drush'