You would insert it at the end of the URL in the browser address bar when using the calibre server to access your library using a web browser.
Code:
[I.e. http://10.253.0.78:8088/#book_id=12208&library_id=Intake&panel=book_list&sort=author_sort.asc,title_sort.asc
This shows my Intake library sorted by author and then title. As @mdclanahan said, a bit clunky but it works.
To do the same in calibre, click on the Title to sort by title and then click on Author(s) which will sort by author maintaining the sort by title for each author as was mentioned the the first message in this thread.