First of all, make sure you level the build plate so that the part DOESN'T stick too well to the platform. WARNING: If the part is stuck too well to the print bed, you run the risk of messing up your extruder head. Make sure the part is loosely adhered to the plate after you pause the print for the next step.
Once the print has finished printing the car section of the print, pause the job and flip the rear wing of the car up. This will make the part taller than the extruder head, so that once the hovering line in the CAD file gets printed, it will push however many cars you put on the build plate out of the printer.
Watch the video on it here: https://www.youtube.com/watch?v=iaZVLy8YHoA&feature=youtu.be
Or read here: https://wordpress.com/post/84694066/63/