After reading the API.
My best guess is, initialize it using
j_obj.draggable();
and from there you can enable it ( set by default ).
j_obj.draggable("enable");
or disable it using
j_obj.draggable("disable");
where j_obj is the jquery object.
This works, but I kind of guessed after scrolling through the api here:
http://api.jqueryui.com/draggable/
I just wanted to verify that these 3, and only these 3 steps are required when you want to be able to enable and disable draggability as needed.
Basically an initialization of sorts, and then an enable and disable method.