Are you sure that makes any difference? It's relatively easy to make a simple additively blended effect look like it's glowing. You wouldn't get actual lighting effects from it, but it doesn't require using any special glow effect mode to make an effect look like it's glowing...

For example, this beam that I made a long time ago when I was fiddling with beams, looked rather similar in-game (of course, the in-game effect version was animated and didn't have the background stars on it, but that's irrelevant). On that, the beam texture (frame) is essentiall pasted on top of the star background, and then I made black transparent (similar to what additive blending mode does on effects). The point is, additive blending is well enough to make a glowy effect happen. You can't get make the screen brighter than (255,255,255) anyway... just bake the glowyness onto the trail texture and it should work. At least by my limited understanding of FS2_Open, it should work.
