Make stencil mask transparent on render target.

I need to render the scene from the player’s view on a render target, but without the player’s hands. I have a Scene Capture 2D on the player and have an assigned render target. The Scene Capture 2D has a post-process material that has the player’s stencil mask.

Post-process material

Render target

The current render target masks out the player’s hand, but it leaves that area white. How can I make the white area completely transparent, as if the player’s hand were never there?