(defn setenv [k v]
  (doseq [c (.getDeclaredClasses java.util.Collections)
          :when (= (.getName c) "java.util.Collections$UnmodifiableMap")]
    (let [f (doto (.getDeclaredField c "m") (.setAccessible true))
          env (System/getenv)]
      (doto (.get f env) .clear
            (.putAll (assoc (into {} env) k v))))))

Generated by Phil Hagelberg using scpaste at Thu Nov 3 17:59:26 2011. PDT. (original)