I think the short answer is no.
The closest I could think of was to combine importance and urgency (other ways may exist)
If you create your own custom view and use the 'group and sort', 'group by...' options you could
create a view that sorts by importance, then urgency.
Once you've created the custom view, you can't drag them about, but you can go to the task and bump up the urgency on one of your tasks.
Then two tasks of equal importance will appear together, but the one with higher urgency will appear first.
