Cheers, I had a dark blue card as a base and backdrop, then put two bit of dark card at the sides, then focused locked, and set the shutter time to 1 second at ISO 100, at F4 ... then turned the lights out and hit the shutter, while open I handheld the flash and fired off two flashes behind and pointing down to the rear of the glass.
The dark cards at the sides puts a dark outline on the reflection, cant explain how, its just an idea I recall from years ago in a magazine.
Hope it helps, wanna share yours ?