It's easy to make it.
Simply add dropshipping service on the page of your shopping cart content. In detail, add the product to your cart, then go to check out, on the check out page, there are some icons eg, remove one product, continue shopping, and check out icon. Under the product list, there is a line of words with a hyperlink, it's "add dropshipping service" 0.01$, it's a product page, ID : 8888 , http://www.budgetgadgets.com/-p-8888.html , so please add the item to your cart to. And if you don't want to add the dropshipping item, please at least leave a note to our customer service, simply as 'dropshipping" is ok.
Thanks for doing dropshipping with us.