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" );
                }
            } );
        }
	' );
}

@j-niell try hooking the above action to the wp_footer e.g.

add_action( 'wp_footer', 'woocommerce_variations_sold_out_filter' );

Hi, this is not working on WooCommerce 2.0+. Is there a way to fix it?
thanks

I just used the code that aplatform commented on for April 1st. And it works just fine. Sooooooo awesome!!! In functions file (or includes file if that is what you choose to use, place):

add_action( 'wp_footer', 'woocommerce_sold_out_filter' );
function woocommerce_sold_out_filter() {
?>
<script type="text/javascript">
(function($) {
// disable and add 'sold out' to product variations
var product_variations = $('form.variations_form').data('product_variations');
if (product_variations) {
var attribute_name = $('form.variations_form').find('select').attr('name');
$.each(product_variations, function(key, value) {
if (!value.is_in_stock) {
var variation_text = $(".variations option[value='" + value.attributes[attribute_name] + "']").text();
$(".variations option[value='" + value.attributes[attribute_name] + "']").attr('disabled',     'disabled').text(variation_text + ' - Sold Out');
}
});
}
})(jQuery);
</script><?php
} 

Oh, and make sure you go into your woocommerce settings->products->inventory and that the box for hide sold out items is unchecked.

Thank you so much for this I have been looking everywhere for code that works!
However it doesn't seem to work so well when you have multiple variations like colour and then size. Say I have 3 sizes of the one colour and only 1 size is available it will show sold out 2 times but not let me see the last size available. Anyone have a fix for this? Would you like me to post a link?

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.