Show Woocommerce minicart widget in checkout page sidebar? And, how to make this update secure by overriding widget?

Before asking question here I want to tell that I have already asked the question in stackoverflow and wordpress forum but have not got any answer. So finally I came here.

I have installed the woocommerce plugin in my wordpress 3.5.2. Everything is fine with woocommerce. I have made a folder called woocommerce and have pasted all the files inside the woocommerce template files inside my template folder. But there is something that I am totally stuck on. In the woocommerce checkout page I want to show cart totals in sidebar. But it is not showing there. In other pages it is working fine. So can someone kindly tell me what wrong here? Any help and suggestions will be really appreciated. Thanks

Update

Here is the screenshot for the woocommerce cart widget in sidebar which can be shown in all pages except the checkout page.

Edit:
Additional, how to make this change secure from updates?

The cart widget isn’t showing because it’s configured to not show on the cart and checkout page. If you want to change that take a look at class-wc-widget-cart.php, there you find the following line:

if ( is_cart() || is_checkout() ) return;  

Change it to:

if ( is_cart() ) return;  

To show the widget on the checkout page.

Note: This will be, if done in the plugins/woocommerce/classes/widgets folder, overwritten on updates.

Edit: Additional information how to override widget and make changes update secure
Source: http://www.skyverge.com/blog/overriddin-woocommerce-widgets/ (Option 5)

1. Duplicate class-wc-widget-cart.php;
2. Copy the duplicate into a folder inside your theme, for example: cust_woo_widgets
3. Make above changes to the file;

4. Additionally make the following change to the widget duplicate:

   class Custom_WooCommerce_Widget_Cart extends WooCommerce_Widget_Cart {
     function widget( $args, $instance ) {
   // copy the widget function from woocommerce/classes/widgets/class-wc-widget-cart.php
     }
   }
   

5. Put following code into your functions.php:

   add_action( 'widgets_init', 'override_woocommerce_widgets', 15 );
   function override_woocommerce_widgets() { 
     if ( class_exists( 'WooCommerce_Widget_Cart' ) ) {
       unregister_widget( 'WooCommerce_Widget_Cart' ); 
       include_once( 'cust_woo_widgets/widget-cart.php' );
       register_widget( 'Custom_WooCommerce_Widget_Cart' );
     } 
   }
   

Note: See source for more information; untested.