I wouldn't worry about the semantics of "securely fastened". I'm pretty sure no cop would ever give you a second look if you actually have a plate where it's supposed to be. Does anyone honestly think they'd take the time to scrutinize the mounting method? Highly unlikely.
This tape is amazingly effective and holds up well outdoors. Don't use too much or you'll never get the plate off again without destroying it or the bumper. I'd start with a couple of 2" strips and go from there.