Here's an
action chain that
might do it. You'll need an extra step though:
1. Install Action Chains and
import the file.
2. Pick a book to test it on and run it on that book.
3. Open the MDE and use the "set authors from author sort" (on a button to the right of the field).
I can't 100% guarantee you'll get expected results though. I'm also not sure if there's a way to bulk-set the authors from the sort.