UseCases not posting to UI by default

What if a UseCase (interactor) is not meant to post (just) to UI?

Assume we have to add a GetMoviesNames interactor that returns only names. It makes sense that it would use the existing GetMovies interactor and then apply more logic to the result to get the list of names only. How would this be achieved with GetMovies only posting to UI? Is there a way to make posting to UI optional so that UseCases could be consumed by other UseCases in different thread than UI?