iAd fallback to AdMob

Hi,

I am trying to get my iAd code (which is working perfectly), to fall back to AdMob (using Prime31's plugin) when there are no ads being served from Apple.

Here's the code I am using:

 #pragma strict
 
 import System.Collections.Generic;
 
 // Bard iAd
 
  var banner:ADBannerView;

 function Start () {

 // Bard iAd + AdMob + Chartboost
 
     StartCoroutine(ShowBanner());
     ChartBoostBinding.showInterstitial( "default" );
     AdMobBinding.init( "a1518d4a265caae", true );

 }

 
 function Update () {
 }
 

 function Awake () {
     ChartBoostBinding.cacheInterstitial( "default" );
 
 }
 
  
 
 function ShowAdsChartboost () {
 
     ChartBoostBinding.showInterstitial( "default" );
 
 }
 

 // Bard iAd
 
 function ShowBanner() {
 

     banner = new ADBannerView();
 
     banner.autoSize = true;
 
     banner.autoPosition = ADPosition.Bottom;
 
     Debug.Log(banner.error);
 
     while (!banner.loaded && banner.error == null)
 
         yield;

     if (banner.error == null)
 
         banner.Show();
     
     else banner = null;
 
 }

I tried changing a part of my ShowBanner function to:

if(banner.error == false) {

     banner.Show();

 } else if(banner.error == true) {

     AdMobBinding.createBanner( AdMobBannerType.iPhone_320x50, AdMobAdPosition.BottomRight );

 }

But that didn't work on the device... Has anyone done this? Would love to get some tips on this.