And now that I've had a chance to fire up Poser and try out my off-the-cuff idea... whaddayaknow, it works. Thanks for the ambient and transmap tips, I tried them and it does make a better-looking beam.

One extra thing I tried that works very well with a bit of tweaking: add a spotlight parented to the base of the cylinder, colour matching the beam, with a very narrow beam width, less than 1° if you can get away with it. With no postwork needed, it adds the little spot of light to what I've heard described as "the ultimate point-and-click interface"...