Baking position using high poly mesh

I want to be able to generate a height map using the highpoly version of my mesh. Baking the position map seems like that would be the best way to do it, but it only encodes the position of points on the low-poly mesh, and there aren't any options to grab it from high poly. 

I've attached 2 pictures below to help explain this, basically I want to create a texture for the second model that reflects the relative height of each point in the first model. Is this possible somehow?