Go past the turnoffs for Keahole and Hawaii Kai Sts. Past the street for Costco. You pass the shopping center on the left and you get to the intersection with Lunalilo Home Road. Go right, i.e. toward the water. You're now in Portlock.
Rich people live here, so beware of funny looks.
The route that I usually take is this. The road is still called Poipu. After that, don't take the 1st or 2nd left, but the 3d left. This will be Lumahai Street. It sort of curves off to the right, and that's what you want.