If you want that, you have to start FCGI application manually with a FCGI spawner.
LSWS will start FCGI apps on demand, but did not stop them when there is no request to process. Maybe we will add a feature to stop unused FCGI app. Some FCGI apps exit after handling certain number of requests.
LSWS did not do anything special in FCGI process management for mass hosting environment yet, but we will do if there is enough interest in using LiteSpeed in this kind of environment.
Right now, we recommend LSAPI over FCGI when possible, LSAPI has better process management in nature.