It shows a giant message in the corner that says that it's on when it's on, so it's super unlikely we'd ever ship a build with it on. And everyone who loaded the game would see the message immediately and yell at us, rather than wondering why lag was so bad.
In terms of how we pulled it off: it's supported by the underlying lidgren network library, so we just had to turn it on. No coding wizardry on our part, it was already there.