In the internal renderer, it's possible to turn off the diffuse on a light source while leaving on specular:
which gives the neat effect of only rendering the highlights on an object:
To my understanding, Cycles emulates real world physics in that the object's properties control how light interacts with it and the light itself doesn't play as much of a role. So I'm curious if there's a way to manipulate an object in Cycles so that it only shows highlights of any light source to simulate this effect?
I've seen some questions on the topic of specularity in Cycles, but only about adding it to light sources, not as a hypothetical solo source.