PayPal API How To Question

We recently wrote some code to create subscriptions on PayPal (https://developer.paypal.com/docs/api/subscriptions/v1/). I am interested to setup a shopping cart where I can have one recurring subscription with the ability for the user to purchase additional products at the same time. Is there a way I can add one time purchases on to a recurring subscription plan the first time it is charged? I am not looking for No as the answer to this question. I want a API references that describe how this is possible. I must be 100% satisfied with all answers to my questions. I don't see the chat lasting more than 20-30 minutes. Please bid accordingly. Write GURU77 in your bid description so I know you read all this. Thanks!