adsanity_ads_posts_sortable_by_{$orderby}.php

<?php
/**
 * Adds new responsive ad unit sizes to the selectable options when creating an ad
 */
function example_adsanity_ads_posts_sortable_by_clicks( $vars = array() ) {

	$vars = array_merge(
		$vars,
		array(
			'meta_key' => sprintf( '_clicks-%s', mktime( 0,0,0, date( 'n' ), date( 'j' ), date( 'Y' ) ) ),
			'orderby' => 'meta_value_num'
		)
	);
	return $vars;
	
}

add_filter( 'adsanity_ads_posts_sortable_by_clicks', 'example_adsanity_ads_posts_sortable_by_clicks' );