Unfortunately weight training works best if your muscles actually move instead of just stretching. I do wonder whether the "trying to lift your car" exercise routine would eventually build your muscles, though.

The other thing I wonder is whether you can do weight training without weights by pitting one hand against the other. Try to curl your biceps on one arm while pushing down with your other hand to try to prevent it. Is there any reason this won't work? Could be a good way to build muscle while sitting at your desk.

Trying to lift a car probably would eventually build some muscle, though as its not a full range of motion, it'd be weird, but I can't see how you'd be able to keep working at it without doing some serious damage to your back. Good luck maintaining proper form while attempting it!

And yes, I know it was a joke :)