forget spambots, how to deal with human spam ?

i was offered a chance to run a contest on one of my blogs

it was a 5 day deal and the winners were picked in a fair manner based on a bunch of factors.

now one dude keeps manually commenting again and again claiming he should have been the winner although he was not. i made the mistake of approving his first comment or may be hes spammed b4 .. wordpress was fked up and letting his comments thru even though i had spam karma running and had moderation enabled. this was just the beginning .. this dude has been on a spamming spree under diffwrent email ids and IP addrs so cant block him easily .. i took down all of his comments after users requested me ..

the silence lasted for a couple of hrs and our man is back spamming..
has anyone dealth with such a situation on ur blog/site ?
any ways to take action against him ?