Yea I didn't think so. But I was kinda hoping, lol
well you could......no it wont work, or maybe.....nah that wont work either....sorry but i can't think of a way this can be done.
I got one idea that more than likely wont work.
Make a target a 2D image. Place the target on the right side of a 1024x256 canvas (canvas width determines the distance target will travel so you have to adjust it). Add alpha channel to the image, so you mask out everything but the target.
Now I got absolutely no idea if this would work. But if you apply a shader to this image that will make parts of the image painted black by the alpha channel transparent, add surfaceparm missile clip to it, i think the transparent area should not stop bullets but the target itself will (again i have no clue if this will work, probably wont).
Add tcmod scroll to the shader, so the target moves in desired direction, and i think you MIGHT have a working moving target that can be used for a button.