WooCommerce - Disable and add 'sold out' to a single WooCommerce product variation dropdown

functions.php

add_action( 'woocommerce_before_add_to_cart_form', 'woocommerce_variations_sold_out_filter' );

function woocommerce_variations_sold_out_filter() {
	// disable and add "sold out" to product variations
	wc_enqueue_js( '
	var product_variations = $( "form.variations_form" ).data( "product_variations" );
        // dont disable with multiple drop-downs
        if ( product_variations && $( "form.variations_form" ).find( "select" ).length === 1 ) {
            var attribute_name = $( "form.variations_form" ).find( "select" ).attr( "name" );
            $.each( product_variations, function( key, value ) {
                if ( !value.is_in_stock ) {
                    var $variation = $( "form.variations_form" ).find( "option[value=\'" + value.attributes[ attribute_name ] + "\']" ),
                        variation_text = $variation.text();
                    $variation.text( variation_text + " - ' . esc_js( __( 'Sold Out', 'woocommerce' ) ) . '" ).attr( "disabled", "disabled" );
                }
            } );
        }
	' );
}

You are my hero!!!!

@MysticsWeb little late on this, but it doesn't work on multiple variations or drop-downs. Ive updated the gist to reflect this.