Better than a boycott:
Everyone should go to their closest Nike Store or Nike Factory Store. Pretend to shop. Load up the cart. Try on several pairs of shoes. Decide to buy 5 or 6 pairs, along with clothing etc.
When you get up to the checkout counter, tell them you changed your mind because of their support of Kaepernick. Then just walk out.
If enough of this happens, word will rapidly reach the idiots up in Beaverton.