For anyone else's benefit, just use datasources, which clojure.java.jdbc supports. We already were where connection pools are used, but we have some apps that don't use a pool, but they can still work using a datasource.
For those apps, we're using next.jdbc's get-datasource function to create the datasource (which contains the above changes so we can use a jdbc uri with properties, thanks!), but using that datasource with clojure.java.jdbc, until such a time comes when we can migrate.