[Jellby]

Yes, replacing spaces with non-breaking spaces works, and it can be done with a plugboard:

Format: any format
Device: KOBOTOUCH (check which one is correct with your device connected)
Input template: {author_sort:'re($, ' ', '_')'}
Target field: authors

Note that the '_' in the template should be a non-breaking space, but apparently I cannot write it in the forum (it is automatically replaced by *). You'd probably have to copy-paste it from somewhere else, or find a way to input it.

With this, if I got it right, the Kobo should sort the authors exactly as your author_sort field in calibre is displayed. You can also modify the database on the device with the Kobo Utilities plugin, make sure to check the "use plugboard" option.

(By the way, the Kobo does something similar with the titles, it automatically sorts them by removing the article "The". A similar trick could be used to make sure the titles are sorted as they are written)