Hello! I'm afraid that to keep things as optimised as possible, all the lights and shadows are rendered to a single surface which is then rendered to the screen. This means that both light and shadow are either aove or below the rest of the instances being drawn. That said, it may be possible to intercept the drawing and have an intermediate step where the shadows are drawn, then the instances you want, and then the lights, all to the main Aura surface. It would mean though that you would have to move all your instance draw code into the Aura draw code... I'll investigate at the weekend and see how that would work. :)
(I'd do it before the weekend, but I have work and no free time 'till saturday, sorry!)