author sort as a column can be displayed, as you discovered, by creating a custom column with template author_sort. I dont see why any other approach is needed.
I have no idea what you mean by saying that you cannot add author sort as a user defined column. You can add anything as a user defined column and give it any name you like. For example, if you type author_sort as the name of the user defined column, you will get a user defined column named #author_sort
All user defined column names must start with #.
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