jreinke/magento-improve-api — pull request #2 by jdurand (2012-12-19 00:09:01+00:00)
Title: Choose attribute for configurable product

Added the option to choose on which of the available attributes you want to base your configurable product. For example if you had a product that has size & colour as available configurable attributes and you just wanted to base your related simple products on the colour you would add one (or more) configurable attributes to the additional_attributes like this :
'additional_attributes' => array(
array(
'key' => 'config_attributes',
'value' => 'some_attribute_code'
)
),