Firstly, have a look at
https://www.mobileread.com/forums/sho...d.php?t=244593 and
https://www.mobileread.com/forums/sho....php?p=2380874 for some discussion on how the Kobo devices sort on the author.
[Moderator note: the thread has been merged with the first one mentioned]
From that, you would have to make changes to the name to sort on first name. You would either need to send the name reversed (as "LN FN" with out a comma) or remove the spaces so the name was one word. Sending the names as "FN_LN" would probably work and should be possible with a plugboard in calibre (and no, I don't know how).
When I see questions like this, I am always curious about why. Wanting to sort authors by their first name seems wrong. Any particular reason for wanting to do it this way?