allow_data_atts.php

<?php
add_action( 'init', 'mf_allow_data_atts' );
function mf_allow_data_atts() {
    global $allowedposttags;

	$tags = array( 'div,a,li' );
	$new_attributes = array( 'data' => array() );

	foreach ( $tags as $tag ) {
		if ( isset( $allowedposttags[ $tag ] ) && is_array( $allowedposttags[ $tag ] ) )
			$allowedposttags[ $tag ] = array_merge( $allowedposttags[ $tag ], $new_attributes );
	}
}