I have had good success using an eraser to clean ink off hard rubber pens. Use the gentlest erasers meant for taking off pencil marks by the process of kneading off the paper, I believe these are called gum erasers. After the stain comes off, the portion of the pen will look dulled but you can rub some oil from your forehead or small amounts of olive oil on it and rub evenly with a cloth.
The same process has helped me take out ink stains from plastic pens as well….