Can I alter the main loop to ‘orderby’ a custom callback?

I have a custom post type where the title is a name, and I want to sort the loop by the last word in title, the surname.

I can easily break the names apart and filter by the last word in a custom query, but I don’t want to re-write the main loop / pagination for the archive page. Is it possible to pass a callback to the orderby param in the action pre_get_posts or is this a lost cause?

Thanks!