Our doctor is a sole-proprietor and has an individual NPI and EIN. He is hiring a new associate physician who has just finished her residency and also has an individual NPI. Since the new physician is an employee and paid by salary, can I bill using her NPI under "rendering provider" (box 24) and then use the owner's individual NPI for the billing provider (box 33) even though it is an individual NPI or do I have to have him get a group NPI even though he is not incorporated?