You gus crack me up.
I have *never* owned a car that used more than 2 screws to hold the plate on.
I think if this really worries you, then you must not have enoough real stress in your life, lol. (ughdance)
hell, my 4Runner currently has 1 screw holding the plate on, which I bummed from a buddy's car the day I bought it so I could drive home. Just this evening I had to straighten it.
more seriously - there is an even easier solutioin. just put some velcro onto the bottom back of the plate, other side of said velcro on hatch. Done, no rattles. In fact if you get Industrial Strength, you can even remove the top two screws for a nice "clean" look. My buddy has done this for many years (hm since I stole his screw, hahaha)