UICollectionView insert cells above maintaining position (like Messages.app)

By default Collection View maintains content offset while inserting cells. On the other hand I'd like to insert cells above the currently displaying ones so that they appear above the screen top edge like Messages.app do when you load earlier messages. Does anyone know the way to achieve it?

This is the technique I use. I've found others cause strange side effects such as screen flicker:

    CGFloat bottomOffset = self.collectionView.contentSize.height - self.collectionView.contentOffset.y;

    [CATransaction begin];
    [CATransaction setDisableActions:YES];

    [self.collectionView performBatchUpdates:^{
        [self.collectionView insertItemsAtIndexPaths:indexPaths];
    } completion:^(BOOL finished) {
        self.collectionView.contentOffset = CGPointMake(0, self.collectionView.contentSize.height - bottomOffset);
    }];

    [CATransaction commit];

James Martin’s fantastic version converted to Swift 2:

let amount = 5 // change this to the amount of items to add
let section = 0 // change this to your needs, too
let contentHeight = self.collectionView!.contentSize.height
let offsetY = self.collectionView!.contentOffset.y
let bottomOffset = contentHeight - offsetY

CATransaction.begin()
CATransaction.setDisableActions(true)

self.collectionView!.performBatchUpdates({
    var indexPaths = [NSIndexPath]()
    for i in 0..<amount {
        let index = 0 + i
        indexPaths.append(NSIndexPath(forItem: index, inSection: section))
    }
    if indexPaths.count > 0 {
        self.collectionView!.insertItemsAtIndexPaths(indexPaths)
    }
    }, completion: {
        finished in
        print("completed loading of new stuff, animating")
        self.collectionView!.contentOffset = CGPointMake(0, self.collectionView!.contentSize.height - bottomOffset)
        CATransaction.commit()
})