Enable local playing even if server is accessible?

Issue description: Is there an option to force playing locally even if the server can be accessed? Sometimes due to NAT setup the server may be accessible, but you may not be in the same room. It would be nice to be able to force playing locally, maybe for instance by a long press. Maybe that could even be a default if the server is not on a RFC1918 address?

Barring that, is there a way to force local playing? Right now this only works for me of I toggle mobile data and wifi off.

Just click the cast button and select local player.