[Moo] Drag.Move using scrollable div as droppable

[Shannow]

I found that using nested lists in a sortable was a limitation of the
class so I created my own drag.move routine.

All is going fine but i've hit a problem that I was experiencing in
sortable list.  As you have to define the droppable element when you
create the new Drag.Move instance, as my droppable div gets bigger,
you can only ever drop elements into the original size of the list.

I have tried this but doens't work:

function getUpdatedAssList() {
    var assignList = $('assignList');
    return assignList;
}

 var newDrag = new Drag.Move(el, {
    handle: el.getElement('span.handle'),
    droppables: function() {
         getUpdatedAssList();
     },

The droppable option takes an element, so using the javascript method
scrollHeight I can get the total size of the div including the hidden
bit but how would i then go about feeding it back into my drag move?

Thanks in advance.