Your purpose is slightly different from what we intend the Port option for. In our mind, it was just for testing purpose when people want to switch from Apache to LSWS, two servers can co-exist on different port during the test period and make sure everything work properly on LSWS, then turn off Apache, and switch LSWS to the production port.
You want to run both in production and let people choose which one to use, it is an interesting idea, but I am sure how well it will go in real world application as it may not save much on system resources by doing so.