That's what I did... I also used electric tape and taped the cotton between the gaps. It's working like a charm. Now it's too quiet!

 

I sound deadened my 99 accord with Quick Roof, also used the stuff and applied it on the entire back of the plates. I'll use the same on my Fit's plate is it rattles. No messy two sided adhesives tapes.

 

I just put 4 screws in to stop the rattle myself. I recommend getting phillips head license plate screws from an auto parts store. I don't think the plastic inserts are threaded so the M6 x 16mm screws are less than fun to put in. I started by sticking the screwdriver #4 in and turning it a bit to widen the hole. Then the screw will kind of thread itself although its not easy. I recommend putting the screws all the way in then backing them out before trying with the plate on. Plate is on good now and no rattle.

 

this... and add rubber washers to the backside of the plate, nobigdeal.

 

I also did this.. works great! no rattles back there and its been over a year and a half now