Magento Checkout Flow Adjustment

I have installed a One Step Checkout extension (from AheadWorks) that changes default checkout flow allowing not logged in customers to go from shopping cart directly to one step checkout page that shows all information in one view (see “Current Flow” slide in attached file). I need to adjust checkout flow so it shows the Register/Login view (the one that is shown as first step of Magento default checkout process when you get there not logged in) before you get to the One Step Checkout page (see “Expected Flow” in attached file). Once changes are implemented, customers should be required to choose between Register, Login or Checkout as Guest before being taken to the one step checkout. In other words, I need to maintain the first step of Magento default checkout for not logged in customers and leave the rest in the One Step Checkout view that is already working. Changes must be implemented first in testing website ([login to view URL]) and if ok moved to production ([login to view URL])