How to use a static cube map with water4 pro?

I noticed the realtime reflections on the water4 for unity4 pro is too heavy on performance since it has to draw all the polys twice doubling my poly count.

How can I add a static cube map to the water as it's reflection instead? Isn't that what most games do for their water? Not sure why they wouldnt have already had it as an option for water4