How to scroll UICollectionView cells before animated insert of new cell?

Question

I have a horizontal scrolling UICollectionView to which I want to add multiple cells that will cause a 2 stage animation to occur:

1. UICollectionView scrolls existing cells to the left, showing the empty space where the new cell will appear, then...
2. The new cell to be inserted then scrolls up vertically from off screen into the empty space.

Imagine the Cells as cards appearing from the bottom of the screen when a user triggers an action.

Currently I have a custom UICollectionViewFlowLayout with an overridden initialLayoutAttributesForAppearingItem which will animate the scroll up element of the transition, however after the first item this animation occurs offscreen. I cannot figure out how to scroll the UICollectionView to the left to show the space where the future cell will appear before the slide up animation occurs.

I have dabbled with contentOffset changes, however this results in some very jerky and glitchy behaviour.

Whats the best way to approach this?

Current `initialLayoutAttributesForAppearingItem' implementation:

 override func initialLayoutAttributesForAppearingItem(at itemIndexPath: IndexPath) -> UICollectionViewLayoutAttributes? {
    let attr = super.initialLayoutAttributesForAppearingItem(at: itemIndexPath)

    attr?.alpha = 0.0
    attr?.transform = CGAffineTransform(
        translationX: 0,
        y: self.collectionView!.bounds.height
    )

    return attr
}