Can I add a vendor to the list without selling their products?

I’ve got some custom code in my theme that’s specific to particular vendors. Some of the vendors listed don’t have any active products at the moment. I want to make sure that the code works when they get products eventually, but that means the person adding the product will have to put in the vendor with the exact spelling used in the code. I’d rather just add the Vendor to the list now so they can pick it instead of hand-entering it. Is there a way to put a vendor into the dropdown even if we’re not selling anything of theirs right now?