Custom Skyboxes in HDRP without cubemaps

Has anyone custom skyboxes running in HDRP? All I want is to make the 3d skybox working again which was a seperate room rendered by a SkyCamera.

Before HDRP it was rendering the sky layer and then the world which opened up a lot of tricks to be used. In HDRP we shouldn't use camera depth layers. Why? Because the performance tanks as it's not made for multiple passes.
So it seems I have to use the HDRi sky but this only uses cubemaps or cubemap parameters.
When rendering to cubemaps in realtime the performance tanks again. Ok, same case as I mentioned before with camera depth layers.
This doesn't seem to be the case with Reflection Probes. They don't tank my performance but I can only render into a Texture of the type cube.

But HDRi sky doesn't take a cube texture as input and playing around with Shadergraph I'm also not finding anything to render my cube texture.
So how can I get this working?

Best thing would be to have a seperate material to have the skybox reflected but I'm okay with having the standard skybox too.
Any help would be appreciated.

Thanks!