i know OSL is around the corner and this might become obsolete very soon, but i tried to build a Fresnel Assembly. As you can see in the pictures the results are a bit different than the built in Fresnel but you can use is as a map to control a mix material and type in the desired IOR. I'm not so good with math so i would be very happy if someone could look into the formula and improve this assembly.
I hope you like it!
