How to get an alpha channel trough Custom Stencil Buffer?


I’m wondering how I can get an alpha channel through a Custom Stencil Buffer.
As you can see I made a Post Process Material to get a Custom Stencil for the central mesh you can see in the viewport. The idea is that this should be used as an occlusion object in Virtual Production, where it renders as alpha so it cuts out from the background. But I don’t know how the Stencil can be rendered as alpha.

Anyone who knows the answer to this question? This would really help a lot!