I take it the transparent Createx idea didn't work out. It was worth a try.
I usually use acrylic washes, but try and get the excess off in about 5 minutes or so. Normally just plain water will work as Robert pointed out.
Alcohol, Windex, any of the thinners or solvents for acrylic paints are going to be harmful to the Future since it's acrylic as well. Not sure what it would do, and you'd probably be better off trying it on some scrap first, but how about Createx Airbrush Cleaner. You probably have some of that around
I had the same problem on my F-105 over the weekend. Some acrylic wash wandered into a place where I didn't get enough Future and the surface was still flat. I finally gave up trying to get it out and shot another coat of gray over the top.