Currently, SecurePoll only ranks elected candidates in STV elections. See the screenshot below
It's useful to rank all candidates, because best losers may be considered as reserves.
And it should be very easy to do so. The sooner one candidate gets elected, the higher their rank; and the sooner one candidate gets eliminated, the lower their rank. So you should generate the final ranking both from top to down and from bottom to up.
All these "unelected" candidates also get eliminated if you continue the count. In each round of counting, you should either elect or eliminate at least one candidate. Since all the available seats have been filled, the remaining candidates can only get eliminated one by one, if you continue the counting process.
You can simply add an option to the software, so that a random selection gets possible. The election admin (the one who does the configurations when creating the poll) may choose to turn it off or on. At fawiki, we use another ranked voting method called Schulze, and we do the potential random selection manually (using page_random field from page table in database, to be more specific), but it would be nice if the software undertakes this task too.