I want to enter free ticket holders to an event without a free option showing up on the website. How do I create this admin only option?
If you only want to have the free registration be available for back-end registrations you should create a price set. The options for admin-only registration types should be in their own price set field, since only price set fields can be marked "Admin only," not an option within a price set field.
Alternatively, if it's just a matter of the participant not paying and you don't have to report on who's a paid participant and who's a comp, you could just register them in the back end and not record a payment. You could still make this work without a price set by creating another participant type of "Complimentary."
You should be able to do this by installing the CiviDiscount extension and using a discount code(s) in your price set for the event.