Vertical scrolling doesn't work when user needs to drag item to position outside of screen?

My page uses the jquery-sortable plugin to allow a user to sort a nested list (only two levels deep) of groups and items. I ran into a bit of a problem with my sortable list when the size of the list exceeds the size of the screen. If the user attempts to drag an item to a group beyond the bottom of the screen, the screen doesn't scroll down to show the desired drop location. You can force it to scroll by using the mouse's scroll wheel while dragging the item but that is awkward and not very intuitive.

I also tried moving the scroll bar to the list and the results were worse. I did this by setting the list's max-height to the size of the screen and specifying an overflow-y of "auto". It still doesn't auto scroll and if you use the scroll wheel you can get to the desired drop location but the plugin won't let you drop it there. I basically can't drop to any groups (my sub lists) that weren't visible when I started the drag.

I really like this flexible plugin though! Thanks.