Assassin's Creed Water Puddles (Help!)

I’m trying to figure out how the puddles of water work in Assassin’s Creed, seems like there’s a planar reflection down, but when you get further away it switches to a cubemap. That solves the problem of reflections not being visible when you’re directly above them, or generally just outside the extents of the planar reflection.

How would I program a material so that it cycles between a cubemap when it isn’t recieving reflection information from the planar reflection, and no cubemap when it is?