It is possible to render a geometry as a blurry object? I was making an scene and thanks to the help of the people here, i managed to make a volumetric light..but now that i think the 'borders' are too sharp, and this light (seen on the picture) is nothing more than a deformed cube, so i need to know, it is possible to for example just select this single geometry and make it look blurry? actually what i need is to make the borders more blurry (like a light), but it could also help me in the future for references. (Oh, and I'm also using Cycles)

If anyone know how to do this, please let me know.
change the object index and use this node setup in the compositor



the id mask will create a mask from the object and  the erode will give it smooth edges