I wish I had an answer for you, but I'm looking for the same thing. Going into the executable (right click .app -> "Show Package Contents") and launching it from there includes the launcher. I can't seem to find a way to just start the game. I suspect it is causing issues with streaming the game to another device.
You are probably on the right track. I don't play on mac but I know this approach works for other applications. I'd go digging around in some of those folders and find the game executable, check Resources folder.