Access to particle parameters in a shader

I have a shader that bypasses (or rather subverts) the built-in rendering mode of the ParticleRenderer. Now I would like to pass extra per particle (per vertex) data to the shader but the only channels I have influence on are position and color and those I already use. (Rationale: I needed this subversion to implement OpenGL-like point size attenuation controls. I had to sacrifice individual particle size for this greater cause.)

Is there some (probably undocumented) way to access some of the particle parameters, e.g. rotation or energy, inside the shader? Or is there a way to investigate this a debugger-like tool maybe?

No, unfortunately such information is not built into the vertex buffers. Currently in Unity all particle operations & transforms are done on the CPU, and the vertex buffer (which is what the shader can access) just has positions, UVs and color.