Put painters tape around the bead on the tire, cut paper or plastic to fit, tape the paper or plastic to the painters tape that is around the bead.
Where I used to work I used to sand blast and paint the wheels of our company trucks. I used to leave the tires on the wheels when I blasted them, then masked them off before paint. They were propane delivery trucks with white wheels. I used to use rustoleum thinned with mineral spirits sprayed out of a gun. Took a long time to cure but held up surprisingly well.