People do this all the time, and you can't stop them, cause it's a video game. Last night I ripped a guys rear off of his plane he's floating for 500 ft. and someone comes in and swoops him, tears off his wing and I got an assist out of it.
So beat them to the punch, when I shoot someone down I'll just lace into them until they explode. This way I ensure I got the most bullets in the guy.
Sucks cause you run out of ammo faster, but I don't land 4 assists as often as i used to for guys I shoot down.
JMFJ