Seems like a good place to plug one of my favorite osx apps, https://www.getcloak.com. Blocks your Wi-Fi connection on open networks until it's able to secure a vpn connection to one of the many services they use (aws, rackspace, etc)
Not quite the same concept, but I setup Little Snitch to work differently on my home/work networks versus tethered phone or untrusted wireless. I originally did this because I didn't want updates running while tethered at a coffee shop. This article got me started: http://www.practicallyefficient.com/home/2014/7/8/little-sni...
