Since the time of posting this original topic, I had this example made
that uses the same scaling trick for pseudo 3d depth (hold the mouse button to shoot and move the plane).
However, I think this is a very troublesome approach, the setup doesn't reflect on the editor and it uses a ton of sprites... It's nice but it's a taxing (both CPU and workload wise) workaround...
There is always LayerToCanvasX("layer",x,y) and CanvasToLayer.
The idea is to translate the X/Y cords from a layer to screen and then back to another layer. This way I could nail the exact same "visiual" coords for many objects on different paralaxes.
The thing is - its a pain in the ass to write in and control. Anyway, my point stands. Missing feature. Something that just doesn't have any reason NOT
to be in the editor. It could and it should. But it isn't.