Here's a solution that I tried out and it works relatively well.
1- Ungroup everything in your car model.
2- Make a copy of the car (if you only need two views, front and side views)
3- Viewing each copy separately in each orthographic view of front and side, use the Artisan knife tool to slice the car in half. Delete the back half of the car in the one model and a side of the car in the other (the idea here is to get rid of any pieces that when flattened into a pancake we do not want to see IE the back of the car...).
4- Use Vertex Tools or any scaling tool that allows you scale an object to absolute flat zero and flatten each instance of the car pieces to the appropriate plane.
Essentially the idea here is to crunch the car by scaling into a single plane but getting rid of the details of the opposite sides when merged together. For your side view you might be able to just scale the vehicle without cutting it in half, but you might end up extra unwanted polygons depending on how well the two sides of the car mirror each other.
