As long as you can get the sides of the airdam to match up ok at the fender wells, you can get a little creative with the mounting of the rest of the airdam. I drilled a couple of holes in the bumber brackets on my 240Z and attached a small makeshift bracket to it. I drilled a hole in the airdam an inch or so above each turn signal light housing to attach to the makeshift bracket. The little bracket will be tough to see because it is behind the bumper for the most part or at least very well hidden by the bumper.
The side mounting points along with these makeshift mounting points will really secure the unit well.