not that simple...if you want your bumper to be flush you WILL have to sand the bondo after putting it on. If you just smear it, it will be a little uneven, far away you cant tell but if you are a perfectionist you would make it smooth. Basically it comes with a bunch of putty and hardner. You mix the hardner in and the Bondo cures quickly in about an hour. If you do use it, wear a mask and do it outdoors cuz the stuff kills your brain.
the bad thing about doing this is you will fill in the holes were your plate holder bolts on. It would be hard to remove if you ever get a ticket and have to put the plate back.
another alternative is to go to kragen,pepboys, etc... They sell plugs for those holes. Luckily for you i saw them in black only. If i wanted to use em i would have to paint them silver, ahhhh!!