Using NSight to capture vertex shader OUTPUT?

I have a WebGL Demo that does a bunch of transformations in the vertex shader.

I want to verify the numerical results against some sample data.

I am able to capture the relevant frame in NSight, and I can view the geometries before rendering, but I cannot figure out how to inspect the output of the vertex shaders. Ideally I would like a tabular record of all the vertex inputs and what the computed output values were.