Copy custom field values to a hidden name field

<?php
// http://www.gravityhelp.com/forums/topic/inactive-column-options-do-not-include-custom-field#post-108400
// Change 243 here to your form ID
add_action('gform_pre_submission_filter_243', 'populate_name');
function populate_name($form) {
    // hidden name field ID 2 holds the name.  2_3 is first name, and 2_6 is the last name
    // custom fields are accessed as an array of values.  Field 1 is the custom field.
    // item 2 of the zero based array holds the first name: $_POST['input_1'][1]
    $_POST['input_2_3'] = $_POST['input_1'][1];
    $_POST['input_2_6'] = $_POST['input_1'][3];
    return $form;
}