I'm not sure how to do this easily. I read this thread when you posted, and couldn't think of a way, so didn't reply hoping somebody more clever would offer a solution.
Here's the problem:
When you select a list of files clustered by Album Artist (either panes, or categories), you only get the list of tracks where Album Artist is equal to the selected value. What you want is to have the query then expanded to :
Find all other tracks where [Artist] = the value of this selected album artist
The query language is a reducing one, not an expanding one (except for the case of the ~a modifier to expand a track into the full album). So if you don't start with the full list, you can't end up with it. But this means you see all Artists, exactly what you don't want.
I can imagine a way to use a relational field, one per artist, to designate certain artists as Major, and others as Minor. This would allow views to be constructed showing only the Major artists. And I can imagine now that this field could be automatically calculated based upon an artist being in more than some predefined number of albums.