Let's just use all U.S. resources available to get every willing non-combatant out of the country of Syria.
It would probably relatively cheap to house and feed every Syrian civilian for a decade compared to the cost of direct military intervention.
Maybe a very-large scale evacuation has never been tried before. But consider this, taking the 22.5 million population of Syria, subtract the 2.5 million who have already left, and the 1 to 2 million (a very rough estimate) potential combatants, that leaves roughly 18 - 19 million civilians to get out of Syria. Or roughly the same population of the greater Los Angeles metro. We should be able to figure out a way to get that many people out.
The combatants would of course be left behind to fight to the last man.