The process pool executor [1] from the concurrent futures API would be suitable to explicitly start and stop the helper process for the `forkserver` mode.
[1] http://docs.python.org/3.4/library/concurrent.futures.html#concurrent.futures.ProcessPoolExecutor
The point would be to have as few state as possible encoded in the multiprocessing module (and its singletons) and move that state information to be directly managed by multiprocessing Process and Pool class instances so that libraries could customize the behavior (start_method, executable, ForkingPIckler reducers registry and so on) without mutating the state of the multiprocessing module singletons.