Transparency for rendered export elements such as shadows or lighting

Many architects export rendered elements such as shadows, lighting or occlusions to use as underlays and overlays with linework. However, VRay only exports these with a black background. For example, if you wish to use these rendered elements under vector linework in illustrator after exporting with Make2D in Rhino, the render needs to be opened in photoshop and carefully masked pixel by pixel. Consideration for all .png exports to be transparent would save significant time in this regard.