GraphicRaytrace from Vive controller to UI panel in the world space?

I have been trying to accomplish using the SteamVR_LaserPointer and physics box colliders on all of my buttons.

But that is non-trivial and causing me lot of issues.

However my UI works fine when using a camera and StandaloneInputModule.
But I have no idea how StandaloneInputModule works.

What I need is a way to do a GraphicRaycast from a Vive controller to the UI plane, then trigger click, drag and caret position events such as would normally be done by the mouse.

This is turning out to be very difficult and I need to get something working!

Thanks.