How do I render a reflection as an alpha channel?

[bpeterandall]

Hey im working on a school project where I have to replicate the egg on the left of the attached image and composite it in Nuke. I have rendered my egg, AO, and shadow as an alpha, but I dont know how to render the reflection as an alpha, does anyone know how to do this?

Image:

[Christoph_Schaedl · Accepted solution]

https://youtu.be/VZiytjt5wD0