I know titch and others on this site have said this is okay to do, but I would not recommend it. The threads cut into the steerer create a stress riser, the bottom edge of the stem creates a fulcrum that will definitely line up with one of those threads, and the stem and bars create a long lever to flex the steerer with. It's a classic case of simple machines and you're just asking to break the steerer off if you ride off road with it like this. It might be fine for casual riding around the neighborhood, but I wouldn't do it.
Here's a much safer option: http://tinyurl.com/3g5whph
or just call around to the bike shops in your area, most shops have at least a few old forks lying around that they would be glad to get rid of.