Start your engines
Fire up Android Player (or any other emulator of your choice that runs Android) in OS X and get the address to the emulator. Click on the settings cog and note the IP Address.
Connect to the emulator
In Windows, open your project in Visual Studio and hit Tools -> Android -> Android Adb Command Prompt. Write adb connect [the IP address] and you should then be connected to your emulator like in the image below.
Run your project
You should now see your device in Visual Studio!
Of course, things can go wrong. The issues I've encountered are these.
1) I had to disable my wireless network while connected to the local wired network. Surely this is a configuration issue that I just haven't bothered with yet.
2) The emulator doesn't show up. Restart Visual Studio.
3) You have to reconnect each time your Mac goes to sleep...
4) Firewalls... Make sure port 5555 is open for TCP from Windows to OS X.