Perhaps an enforcer could work for the role, but I doubt that you could spend enough skill points to get them to move near as quick and stealthy as a Phantom.
Perhaps you could make a enforcer sniper. Hehe, heavy armored sniping bliss.
That gives me a bit of a theory though. Perhaps one of the main purposes of the avenger is to fill in that customized class role. Since I am assuming they will be decent at everything, but not great at anything, perhaps it would be easier to customize one of them.