Control scrollbar behaviour during drag

I noticed in this reorder example on CodePen, that, when dragging en item up/down, the list scrolls nicely further up/downwards when reaching the end of the list. I’d love to implement such functionality for a custom draggable list, but the scrollbar keeps acting like it normally does when scrolling. In the source of listView.js I (supposedly) found the part responsible for scrolling up/downwards, but I can’t seem to figure how to control the scrollbars behavior. Thus:

How can I control the scrollbar behavior during a drag movement, from acting like someone is scrolling (the list)?