Volumetric materials would help but it would increase rendering time. Apparently the guy who made that animation in the link used vertex colors to achieve the look. That's really basic but I don't think we have access to that in the material room directly out of the box. There may be a python or something out there or  maybe BB knows of something that would let you fiddle with them. You'd still need to manually group the spheres though, as we don't have an easy way to do it in Poser. Hmm...maybe a cloud prop would be worth including in the next release?