To do this, you actually need two new fields:
* Artist Sort Manual : This one is a plain string field. This is where you will type your manual overrides.
* Artist Sort : This is the field you will use to do your actual sorting. It will be a "calculated data" type. The expression to use is:
FirstNotEmpty([Artist Sort Manual],[Album Artist (auto)])
It's pretty easy to use. Just change your sorting field in all of your Artist type views to use Artist Sort. Put any of your exceptions into [Artist Sort Manual]. It should all work as expected.
As an experiment with my own collection, I created these fields. As I was looking for something to set manually, I remembered that I have albums by Miles Davis. But I also have albums by "Miles Davis Quintet". When looking through my Artist view, it's mildly annoying to see Miles Davis and Miles Davis Quintet, as I mostly think of them as the same thing (even though they aren't strictly the same artist, I consider them as one).
So, for the Miles Davis Quintet albums, I set [Artist Sort Manual] to "Miles Davis". Then I changed my "Artists" view to use [Artist Sort] as the first category (instead of just [Artist]). Voila'! Now my Artists view groups Miles Davis and Miles Davis Quintet into a single artist for me!
As you can see, this field can be used for several purposes that can make browsing your collection better and easier.
Best of luck,
Brian.