Multiple sizes per slot

dfp-async-mulltisizes.php

<?php
add_filter( 'acm_ad_tag_ids', 'my_acm_ad_tag_ids' );
function my_acm_ad_tag_ids( $tag_ids ) {
    $tag_ids[] = array(
        'tag' => 'flex-leaderboard', // tag_id
        'url_vars' => array(
                'sizes' => array(
                    array(
                        'width'     =>  '728',
                        'height'    => '90'
                    ),
                    array(
                        'width'     =>  '970',
                        'height'    => '66'
                    ),
                ),
            'fold' => 'atf', // %fold% token
            'my_custom_token' => 'something' // %my_custom_token% will be replaced with 'something'
        ),
    );
    return $tag_ids;
}