Convert the guest checkout orders to a register customer orders. If there is no customer account for the guest then create a new one for the guest. Add $60 to install it for you in one day, $120 in half day. This is a Non-exclusive Single Domain License price. Under a Non-exclusive Single Domain License, you are not authorized to redistribute or sell the extension to other parties. Click here to see demo site
You need to checkout one item as a guest, then use 'demo', 'deomo123' as username and password to login to backend. You will see the 'create a customer account' link under the Sales->Orders menu besides your guest name. Then click the link, it will redirect to the Customer main menu.