KB - Make Answers searchable without assigning visible categories

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Hello, 

We have a new custom widget in our knowledge base that we would like to deploy, a tree of categories that will lead the customer to an answer. 

Each bottom level category in the tree will have one linked answer. 

The problem we are having is we wish to have additional articles that are searchable, but are not included in this tree. 

Is there a way to create a hidden category that will allow answers to be searchable, but not actually be visible, or make searchable without assigning a category?

Is there a way to accomplish this without custom code?