I think the method you mentioned is the primary way that you would get it to appear without your name as the author. I did also test and found that you could create the discussion topic within the course where you want it and then use "Copy To" to copy it to the course itself and it would also show with no author. This still requires removing the original one, but doesn't require a separate course to copy from. Using "Duplicate" will still show you as the author. Our school uses blueprint courses to manage content that is used in courses, so they already have a source course they can copy and/or sync from so that they don't show as the author in the live course.
In general, you wouldn't want someone to have permission to say certain content was created by someone else. So, unless you have the ability to "Act as" the teacher, there isn't a way that I know of for you to change the author of the discussion post to someone else that you choose.
Another option to consider is to have one of the instructors create the discussion fully with training/support or at least have them create a placeholder. From my experience, the author will remain the person that originally creates the discussion board, so even if you edit it after they create a placeholder for you to use, it would still show them as the author.