Layered approach is the most suited and practical.
It is used all over the demonstrations on the website
is mentioned on this page as well as in the
automotive pages (car paint, headlight glass, etc).
The
layered material node is not even necessary since the materials themselves have a "material layer" slot on which a dedicated set of material layer nodes can be attached to.
In this case, it's a "double specular materials" setup:
1. first one is the regular specular material with disabled reflection (only refraction)
2. second is the "specular material layer" with default parameters acts as a coat layer
Thus, providing an independent specular reflection and refraction roughness at two distinct levels (base material and the layered material).