Nothing clever needs to be invoked. It's baked into the text of the treaty. Article 5 is what's invoked to bring the whole alliance together to defend against an attack on any one member. However, Article 6 limits Article 5 to attacks within Europe, North America, Turkey, and islands in the Atlantic north of the Tropic of Cancer. Strictly speaking, even an attack on Hawaii wouldn't invoke it.

I guess countries outside that area could join, but without a change to the treaty, the key clause in the whole thing wouldn't apply to them.