Oh yeah, I didn't think of that. Hm, one trick to try is using multiply blend mode for the floor instead of alpha transparency. I'm not sure what effect that'll have, layering a multiply blended texture over a multiply blended base texture, but it's worth a shot.
Another option would be the technique from the "real mirrors" demo. Can't find the link (sorry) but the technique was pretty simple. You render the scene with a camera placed just below the floor facing up (the the floor is made of one-sided polygons it won't interfere with the rendering,) copy this to the texture on the floor, render the scene again from the player's view, and then flip. This is a lot like using cube mapping for reflections, except since the reflective surface is flat and unchanging you can just use regular texture mapping instead of cube mapping.
Another option would be the technique from the "real mirrors" demo. Can't find the link (sorry) but the technique was pretty simple. You render the scene with a camera placed just below the floor facing up (the the floor is made of one-sided polygons it won't interfere with the rendering,) copy this to the texture on the floor, render the scene again from the player's view, and then flip. This is a lot like using cube mapping for reflections, except since the reflective surface is flat and unchanging you can just use regular texture mapping instead of cube mapping.