I'm guessing it could be possible to make a gravity gun that effects bricks.  I'll have to wait to see trace(); before I know for sure though.  It wouldn't be as clean as the gravity gun is with other things though, as it would be able to pick up multiple bricks in a spot, and wouldn't have as good of a reaction when moving things.  It also wouldn't be able to tell if you've even picked up bricks.  Heck, for you it could look like you picked up a brick, and dropped in on a catapult and had fun with it, while to others it looks like your just randomly walking around.