How to get game viewport-only UVs in a User Interface Domain material?

Hi! I’m working on rendering some meshes on top of my HUD. I came up with wrapping my affected widgets into a Retainer Box, applying a User Interface material to it which grabs the CustomStencil texture from SceneTexture as an opacity mask and then just marking the meshes I need to occlude my HUD to render Custom Depth. Of course I’m connecting what seems to be the “Viewport UV” to the SceneTexture node, but that only works packaged, Launch or Standalone, but on any kind of PIE instance, I see disalignment between the CustomStencil mask applied to the widget and the geometry rendered in the game world. I suspect the Viewport UVs in a User Interface Domain considers the entire editor window and not just the viewport the game is being displayed in.
Is there any way to get the UVs for the game viewport only in a UI domain material?

Any help is appreciated!