A dry alternative to Astroturf is orange construction fencing. Personally i'm not much of a fan of this stuff because it's kinda hard to stay in control on it, but it gets the job done. If you can have the fencing on the in-run and turf on the jump it should work good. I'v done that before and it worked just fine without water.
And yes, just put plywood or pallets or whatever you have below the turf, it adds a lot of speed.