Currently there are no airports that I'm aware of that are 100% AIT so you can still get through with a normal screening sometimes. That said, if you're in an AIT line or selected for one, no you can't opt for a traditional screening. You're a suspected terrorist and you can either take your virtual strip search or "enhanced pat-down." The justification being that the WTMD doesn't detect non-metallic weapons, explosives or incendiaries.