Add more native ads to existing facebook scroll ios

I am trying to add more native ads to existing scroll in ios.

FBNativeAdsManager *manager = [[FBNativeAdsManager alloc] 
initWithPlacementID:@"Placement ID" forNumAdsRequested:5];

On initialising I put the 5 to load five ads. But, If user is scrolling through those ads, I want to lazy load more ads and add them to the same scroller.

The class FBNativeAdDelegate is used as a delegate of the scroll view. as mentioned on the link http://ift.tt/1dNKlz5 It contains a delegate which tells that user has scrolled till end.

- (void)nativeAdWillLogImpression:(FBNativeAd *)nativeAd{}

The above method gets called every time when a fresh ad appears on the screen. So I know if this method gets called fifth time, I have to load more ads to it.

But, how to add more ads to it?

Any relevant help and suggestions appreciated. Cheers!