I saw your stackoverflow question and provided an answer there. I’m just cross linking it here incase anyone has the same question.
Here is a twiddle I built that helps demonstrate your question on SO: Ember Twiddle
Certainly there are other ways to do this, that’s just my take.
Also, FWIW, SortableMixin has been removed from Ember 2.x. Even though it’s available in the controller addon, it’ll likely become unsupported at some point in the near future.