You can use Alembic[1] to add dependencies at run time, not just adding them to the path, but downloading them from clojars or maven central, eg. using the example from the docs:

(alembic.still/distill '[org.clojure/tools.logging "0.2.1"])

Or something like clojure/tools.namespace[2] to edit your project.clj and then reload/refresh all namespaces to be current.

[1] https://github.com/pallet/alembic [2] https://github.com/clojure/tools.namespace