Right now, all I can think is that we need to provide pure humanitarian evacuation. Just say, "If you're a decent human being, we're sending a ship to help you. Please, come join us. We have a dozen midwestern states with temperate climates, fertile ground, and vast quantities of unused land. Just leave your weapons behind." If the entire population took us up on the offer, that's 18 million people -- about 5% of the US' current population. If we spread them evenly around the country, that'd be one free city of 450k per state. Settling them would be a huge boom for virtually every industry, from construction on up, because that's a sudden influx of consumer spending. It's also inflation-free, because the people themselves would be a massive lift to the US' economic productivity cap -- the people themselves are providing the economic value that is being spent for them. What state would say no to a free Sacramento, or Atlanta, or Miami?
We'd need to employ countless current citizens as well, of course. Language teaching (actually quite easy, if you aren't hindered by school schedules; just get people to practice every day), job training, computer literacy... the need for good-paying jobs would be exceptional. Of course, they would need to be naturalized, but the President can provide amnesty just like the past two Republicans did. It'd save a lot of time and money that way.
Here's the best part: after we do that, we just... leave Syria. Assad and the rebels are both pieces of shit. Let them kill each other over crater-spattered fields of salty sand. Heck, we'll sell them rockets and mortars, all lightly used. Can you imagine the cities we could build with the wealth we've locked up in drones and artillery and mines and ships and bombs and planes?
The best part of it all is, it's a by-partisan solution, from the American perspective. Obviously the Democrats will back it because they are progressives, and seek diplomatic solutions. The Republicans will like it because it's pro-life AND good for the budget. Win-win.