Nest a Field Widget's primary field in a Fieldset array
I ended-up just adding a submit and validation callback that re-aligned the index.

In the hook_field_widget_form

function mymodule_field_widget_form(&amp;$form, &amp;$form_state, $field, $instance, $langcode, $items, $delta, $element) {
//  widget form logic....

//  Add a custom submit handler to realign the values
    $form['#submit'][] = 'mymodule_option_selector_submit_validate';
    $form['#validate'][] = 'mymodule_option_selector_submit_validate';

//  Tell the form what field uses the option selector so it knows which fields to relign        
    if(!isset($form['#option_selector_fields']))
        $form['#option_selector_fields'] = array();
    $form['#option_selector_fields'][] = array(
        'field_name'=&gt;$instance['field_name'],
        'langcode'=&gt;$langcode,
        'delta'=&gt;$delta,
        'columns'=&gt;$element['#columns'],
    );

    return $element;

}

function mymodule_option_selector_submit_validate($form, &amp;$form_state){
    if(isset($form['#option_selector_fields'])){
        foreach($form['#option_selector_fields'] as $field_data){
            foreach($field_data['columns'] as $column)
                $form_state['values'][$field_data['field_name']][$field_data['langcode']][$field_data['delta']][$column] = 
                        $form_state['values'][$field_data['field_name']][$field_data['langcode']][$field_data['delta']]['filter']['client_selector'][$column];      
        }
    }
}


Still would be nice to know if there is some kind of toggle in the widget form system to accommodate this.