Custom sorting using `postForFeedMeFieldType` with Feed Me

FeedMeCustomSortPlugin.php

<?php
namespace Craft;

class FeedMeCustomSortPlugin extends BasePlugin
{
    // =========================================================================
    // PLUGIN INFO
    // =========================================================================

    public function getName()
    {
        return Craft::t('Feed Me Custom Sort');
    }

    public function getVersion()
    {
        return '1.0.0';
    }

    public function getSchemaVersion()
    {
        return '1.0.0';
    }

    public function getDeveloper()
    {
        return 'S. Group';
    }

    public function getDeveloperUrl()
    {
        return 'http://sgroup.com.au';
    }


    // =========================================================================
    // HOOKS
    // =========================================================================

    public function postForFeedMeFieldType(&$fieldData)
    {
        // This is less intensive than craft()->fields->getFieldByHandle($fieldHandle);
        foreach ($fieldData as $fieldHandle => $data) {
            if (is_array($data)) {

                // If we've got an array of data, a good chance its a Matrix field - double-check!
                $field = craft()->fields->getFieldByHandle($fieldHandle);

                if ($field->type == 'Matrix') {
                    $orderedMatrixData = array();
                    $tempMatrixData = array();

                    foreach ($data as $key => $subField) {
                        if (isset($subField['fields']['order'])) {
                            $order = $subField['fields']['order'];
                        } else {
                            $order = $subField['order'];
                        }

                        $tempMatrixData[$order][$key] = $subField;
                    }

                    // Sort the array by key
                    ksort($tempMatrixData);

                    $fieldData[$fieldHandle] = array();

                    foreach ($tempMatrixData as $key => $subField) {
                        $fieldData[$fieldHandle] = array_merge($fieldData[$fieldHandle], $subField);
                    }
                }
            }
        }
    }
 
}

Add this to a folder called feedmecustomsort in your plugins folder.