There is no function in game designed to do exactly that for you. But you could however do it by giving all the blue AI controled units radio damage at the start, and then make a route for them. That way the blue AI unit locations will only be updated at the start of the scenario, and their new location will only be updated once a human controled unit spots them. It's not exactly what you are looking for if i understod you correctly, but it's pretty close and it should achieve the same things more or less. Just keep in mind that radio damage fixes itself every 5 or so minutes, so you need to repeat the damage for the duration of the scenario.