Use the new kingpin to bash it through, and if you don't have one yet then try the large ratchet bit extender that comes with ratchet sets. (Like this one, it's the 1/2")
Hammer it into the broken off side of the kingpin straight down, hammer on the side that is female.
Place the baseplate on concrete when hammering down, you will get it at least 3/4's of the way out before it touches the ground.
Then use either 2 solid boards spaced out so it can pop through freely, or something with a hole in it that is somewhat pretty solid, aim for putting the kingpin right above that hole - now f'n bang it!
Holding it in a vice is just gunna chew up the baseplate if it starts to slip when hammering down, this way is easier, and requires less tools. I just put up a full quick and easy way of installing kingpins in the other truck kingpin thread.
Installing a kingpin is alot harder than removing one, broken or not. Don't give up. Good luck.