Adding a Variable Product in WooCommerce Programatically

Found the solution to make a product attribute, a variation.
Lets say we have:

wp_set_object_terms( $post_id, 'XL', 'pa_size' );

Above is a custom attribute (a size attribute). In order to make it a variation you need to do this:

$thedata = Array('pa_size'=>Array(
        'name'=>'pa_size',
        'value'=>'',
        'is_visible' => '1', 
        'is_variation' => '1',
        'is_taxonomy' => '1'
        ));
update_post_meta( $post_id,'_product_attributes',$thedata);