Katharsis: String sorting case insensitive

Question

We're using Katharsis to implement the JSON API spec and have a question regarding sorting. It looks Katharsis uses an objects natural order when getting sorting, but is there anyway to override this for a given field? We would like to be able to sort strings in a case insensitive fashion, but looking at the Katharsis docs I can't find a way to pass a custom comparator. It looks like the only option would be to roll our own string class and I'd like to avoid that if at all possible.