I don't really get the point where "dynamics in the traditional sense of the word" is out of the question... I like metal, but if everything is as loud as everything else, I find even the best of songs rather uninteresting. The reason why there aren't many volume changes in metal is first and foremost that nobody seems to use volume changes in metal.
That's mainly due to audio engineering. The drums are perhaps the most dynamic instrument by themselves, guitarists can mimic it using a volume pedal I suppose, as could the bassist, but your vocalist's volume would actually need to be ridden quite hard in the PA by your house engineer. If you go in saying "Yeah, our songs rely on dynamic volume, don't compress us too much," he's gonna HATE you. That makes his job a living hell, even if your bassist is good enough to ride a pedal to match the drum's dynamics, which is rare.
I'm an engineer myself, I know it's though, but it's not impossible. Mainly what you're saying is that sound engineers hate bands that have electric instruments and want dynamics, still outside of metal it's very much possible to do this, one example being Pink Floyd.