I think you'll need to do render passes, such as a specular pass that you can layer on top of your diffuse pass, etc. I already did that, the problem is that it does not come with transparent background, it comes with a black background instead. The only way I can see this working somewhat is if I copy the hourglass' glass body, flatten the copy and then make it provide alpha from the glass' back, so that the specular can be seen while the bg is transparent.