Well, handling is the only way he'll calm down ... just think if you were that lil guy n sum huge creature (us) many times your size was trying to pick you up, u'd do what ever in your power to have that creature leave u alone. He just needs to get use to the whole handling thing. try dead pinkies i find snakes are less agressive on f/t pinks.
As far as him letting go, you should just allow him to let go when he's ready, kings don't really bit and hold on for too long (far as i can remember) you may wanna try a snake hook to get him out of his enclosure to reduce the chance of him biting you or so thick gloves
Hope this helps you.
~ZF