I don't know if it works in ghost, but in every other cod you did it like that:
1. Get a auto gun and freeze your ammo.
2. Scan for value 0
3. Shoot. While shooting search for increased value. (Hotkeys might help)
4. Stop shooting and search for 0 again.
5. Repeat that until you only have some addresses left.
6. Freeze the value of the address at 0. Voila Rapid Fire.
But as i said. I don't know if it works for ghost like that.