I still don't understand that part. Shoot with what? Do you mean hit the powerup with the paddle or shoot it with ball?
If it is ball, you would once again need a game attribute. Create a boolean game attribute with name like <power hit>
Inside <when ball hits special power> event, set <power hit> to true. Beneath that, add <do after [3] seconds > block. Inside that block, set <power hit> to false.
No time to show screenshots now. I'll check again shortly if it didn't work. Please try as much as you can and let us know what it does.