Here is an example : LIVE DEMO
It is not very compatible with your combobox because it catch the mouse click event to display its options, but it is working.
$(document).ready(function(){
var click = false,
top = null,
left = null;
$(document).bind('mousemove', function (e) {
if (click == true) {
$('#draggable').css({
left: e.pageX - left,
top: e.pageY - top
});
}
});
$('#draggable').draggable().click(function(e) {
top = e.pageY - $('#draggable').position().top;
left = e.pageX - $('#draggable').position().left;
click = !click;
return false;
});
$('html').click(function() {
click = false;
});
});