I kill the slugs I find in my worm compost by dropping them into a bowl of boiling water. Seems to kill them instantly, so it's the most humane way I've found to get rid of them... I don't mind them in my worm bin but they use it to multiply and the creep back to the adjacent plants...
Is there any harm, that you can think of, to waiting til the water cools then pouring the dead slugs and bit of water into the bin to compost? We're not talking lots here. Maybe 9 slugs at most at a time.