Maybe he should try another defence...
I think he'll probably end up in a military prison using the defence that the war is unprovoked and illegal (despite the validity of the argument).
However, what if he instructed his defence lawyer that he was not prepared to serve in Iraq because his own forces were pesently operating in a 'lawless' or 'anarchic' manner? By this I mean they are assassinating, kidnapping, torturing, murdering civilians and generally applying force which is massively disproportionate to the task - in contavention of military and civil law and probably the Geneva convention too? The Marines (alleged) recent re-run of Mai Lai and the introduction of ethics instruction for their troops would seem to support such a defence.
He's on a hiding to nothing arguing that the war itself is illegal, but an SAS trooper recently escaped criminal charges when he refused to serve alongside the Americans for much the same reasons as I've described above.
Will be interesting to watch....