I feel like I'm a little late on this one, I hope I'm not too late: forget messing with your bumper... Lots of people where I live (in Ohio) just take their license plate and throw it inside their car on their dash so that it can be seen by cops. Another way to get around this is to just keep a mounting bracket in your vehicle with you at all times, if you do happen to get stopped just tell the officer that you were in a fender bender and are waiting to get it put back on.