You don't need to have the DLC to get this achievement -- I got it using a 4-star Agency SUV and a ramp truck near the agency exit on the first island. Set the ramp truck on the freeway on-ramp and get lots of speed, then launch off and do the flips.
Not the easiest method; took me several tries before I got a good aim on the launch! This video shows the location, though you can't do it in Keys to the City, of course.