I did this on my Galant GTZ, and i just used (carefully) a pair of needle nose plyers and the letters just came off pretty easily with very little residue left behind. I was able to clean that off with a rag and hot water.
I did the same thing on my Rolla and the letters were quite a bit tougher to get off and left quite a bit more sticky residue. Used some Goo Off and a rag and got most of it off. When the car is spankin' clean you can see some remains, but as soon as it gets the first layer of dust / dirt, you can't see anything...
Never thought of floss and a heater