You can do some creative rigging and achieve this in bryce.  Keep in mind I did this example in about 30 seconds,

.....but take whatever object you want to self illuminate, and give it some transparancy,  a little reflection, and select additive.  Next create a light source inside of the object and this is what you get.  With a little more time, you could probobly achieve better quality than what I presented here.

The thing I would have to figure out is how to get soft glowing edges instead of these hard ones.