I did something like that before. I had an Ford Tempo with a broken head light. I used the plastic form the packaging for the mounting kit for a head unit, cut ti to size and it worked great. You actually couldn't tell that much except the "new" one was cleared than the factory one.
An ex-friend of mine once used a similar setup, but hers consisted of a mason jar and mass quantities of duct tape. It worked out pretty good for quite a while. She got pulled over once, but local law enforcement knew who she was...plus she was quite attractive, so that doesnt hurt anything.