how can I disable (not mute) built-in microphone device?

Summary: I need to somehow forcibly disable the built-in microphone device on my MacBook Pro so that it is not even listed in the sound preferences as an option for audio input.

Details: I am using Pro Tools 10 on a MacBook Pro running OS X Mavericks. Sometimes I have my audio interface (Apogee Ensemble) connected, and other times I don't, and am just working using the built-in audio interface of the laptop.

The problem is, when I launch Pro Tools after reconnecting the Ensemble when I was previously running a Pro Tools session using the "Built-In Output", it automatically sets the audio device for output to "Built-In Microphone" for the playback engine, which obviously doesn't work. If I ever forget to change it to "Ensemble" when I launch Pro Tools, or I launch a session directly instead of launching the app on it's own first, I need to quit Pro Tools, reopen it, change the device, and then launch the session again, which is a majorly time consuming pain in the ***.

I have already tried contacting Avid support on this, and that was a massive waste of time, and no help at all.

I'm sure there has got to be some way to disable the Built-In Microphone device in OS X, and a way to re-enable it whenever I need it (like on the rare occasion I make a Skype call). Hopefully some OS X guru out there can reply with instructions on how to do it, and save me from countless hours of wasted time and pulling my own hair out in the future.

Thank you! 🙂

Mike