The multiplier functionality doesn't currently allow splitting.
However, here's a couple of things that might help that we've designed to be quicker than using the multiplier.
Swipe - Try swiping an item button towards the order. Swiping adds the base item to the order quickly, plus any default required mods. This is far quicker than using the multiplier.
Two finger tap - For more complex items with mods added. After the item is added to the order, tap the order item with 2 fingers. This will clone the item.
Check out this and more in our iPad app training videos: