Adding photo elements to 360 spherical projection

Hi,

  I've watched Jama Jurabaev's excellent tutorials about how to paint equirectangular scenes to create 360 VR experiences, using Photoshop's 3D spherical projection tools.

360 Pano Painting Tutorial with Jama Jurabaev

He's a very talented painter so freehand paints his examples, and seems to do all his paintwork directly on the distorted 3D layer.

My own workflows for simple 2D imagery are a lot closer to matte painting, and use a lot of photo elements in a layer stack.

I've tried using Jama's principles to create a 360 VR matte painting, but bringing in photo elements in the projected 3D view places them on a separate layer above the base render (as you'd expect). But when I then orbit the camera to work on a different area, the photo elements don't move with the base layer. Is there a way of linking them to it or flattening them down to it, so they then become part of equirectangular image? Almost like projecting them on to it once they're in place?

Still getting my head round the 3D system. I reckon it should be possible, just not sure how...

Thanks!