Just use the '[Auto Product Display][1]' module which simply Product Display creation process by providing option the create it at the same time with Product creation.

> Features
> 
>  - Provide the Product Display creation form along with the Product    creation form. User can fill that form to create Product Display at   
> the same time with Product creation.
>  - That form, which used to create Product Display, will be the same as    the form when user try to create Product Display manually. So,
> If you    have additional fields in your Product Display node type,
> those    fields will also appear in the form.
>  - If the product is referenced by only one Product Display, the Product    Display content is displayed directly to the form, so it
> will be    automatically updated when you save the product.
>  - If the product is referenced by more than one Product Display, the    referencing Product Displays will be displayed in list, so you can   
> also update the Product Display by clicking the link from that list   
> first.

  [1]: http://drupal.org/project/commerce_auto_product_display