Reflectors and mirrors will give you a three light setup without the expense of buying more lights. The AB800 has more than enough power to handle the lighting for small full length sets.
The downside, is that is seems you are short on time. You'll need to make sure you have enough time to practice with the reflector and mirrors before the shoot. Of course, the same really goes for multi light setups as well.
Here is what I would do to make the AB800 work triple duty. I would get a full length diffuser panel, and a 2'x3' acrylic mirror (lighter than glass and safer). You can then aim the light through the diffuser as a large softbox, but at the same time allow some light to pass the panel toward the back of the set (spill light, or split lighting). Use the mirror to then redirect that light back onto the subject from the other side. Its the perfect intensity as a kicker light, and the light through the diffusion panel acts as a full length main. The difference is usually about a stop or so, which is perfect for the main/kicker lighting setup.
You can also use another silver or gold reflector to further add dimension on the subject using that spill light, from what ever angle you see fit or needs more fill. If you balance it all with ambient lighting, it will be a very nice overall lighting effect.
The other downside is that it will be difficult if you also need to light the car. The reflectivity of the cars surface will cause you lots of issues unless you are lucky, or shoot it outside with a nice overcast or late afternoon sky to create nice smooth tonality on the cars finish.
But for standard full length poses, this technique works really really well.