Everything could be painted, doesn't matter how soft is the material... G-Benz is correct, the secret is the flexing agent.

Four years ago I painted the bumpers from my 300E and their look as new till today.

The bodyshop where I painted them is a STANDOX dealer and they have all the neccesary primers to treat any type of surface.

Before they paint my car I was very concern about how long the paint will last in good shape. To make me feel confortable they painted a rubber ball and a sponge with that treatment, two days after they painted those things I was able to squeeze the sponge and bounce the ball and the paint was immaculate.

Make sure the body shop you choose know about those kind of treatments.

Good luck !