Supplementing iAd Placement with AdMob

I'm having difficulty with creating a system in Unity that can run Google AdMob as a fallback when iAd fails to fill an ad order. The closest thing I've come up with is showing AdMob ads if iAd completely fails to load entirely, not just when iAd fails to fill an order. I've searched extensively for tutorials on how to accomplish this for a Unity project and the only two semi-promising things I can find are the paid Prime31 plugin and a general Xcode tutorial. When looking at my Xcode project after exporting from Unity there is no file called ViewController.h, which the tutorial references.

Can anyone either explain the Xcode tutorial a little clearer from a Unity project perspective or point me in the right direction on how I might be able to accomplish this without having to use paid plugins? I don't have a lot of experience with Xcode outside of just the quick passthrough from Unity to my phone or uploading to the App Store.

Any advice would be greatly appreciated. The Xcode tutorial I'm referring to is here:

http://code.tutsplus.com/tutorials/supplementing-iad-placement-with-admob--mobile-9543