As I mentioned in a previous post:
Pixel perfect means it corresponds to actual pixels on the screen 1:1. What you are trying to do is not pixel perfect by definition.
I'm going to assume that what you want is simply have 1 virtual pixel be a 2x2 on-screen pixel. This isn't pixel perfect, but I assume you simply got your terminology wrong. Open up UICamera.cs, find the drawCallOffset property on line 315:
float mod = (1f / size.y) / mCam.orthographicSize;
You will want to change this to:
float pixelSize = (root != null) ? root.pixelSizeAdjustment : 1f;
float mod = (pixelSize / size.y) / mCam.orthographicSize;