I would, depending on the situation, either enroll them in college, sign them up as Conscientious Objectors, or encourage them to go to jail for their beliefs and hire the best lawyer I could find.
If they didn't want to go, I would even consider moving them to Canada or Mexico.
There is no such thing as a just war.
@Bev B - Just because you were stupid enough to join, doesn't make those who decide not to cowards, no matter how badly you want it. I believe that it requires more bravery to stand up for what you believe in (peace) than it does to blindly follow orders that you haven't thought through. But that's just me.