I do the same - hold the eye of the hook with forceps. It keeps paint out of the inside of the eye but will still get some around the outside of the eye. You can scrape that off easily with a knife blade before you cure the paint in the oven.
You are painting bismuth heads, correct? Not sure if you are using a mixed alloy or pure bismuth, but one thing i have learned is to keep the heat low when you are heating the head to put the paint on. Just hot enough for the powder paint to stick is enough. If the head gets too hot when you are first heating it up, the metal has odd lumps that will grow when it cools down. It sounds strange, but it has happened several times to me on heads made with a mixed bismuth/tin alloy when i left them to heat for too long over a flame.