Maybe as an option we could just ask the submitter to slow down a little. If it's not spam he will probably be respectful of the request. My thoughts are that maybe sometime in the future some hot topic might call for a lot of quick submits—you never know.
Plus to me, I hate to see a forum with freedom of speech tightened down for everyone by iron fisted inflexible code just because of one user, one time. I like this forum a lot no matter how many posts someone makes, but 18 quick posts does seem like a lot to me too. Must be a slow day for him.
Maybe we could send him this: ICMP message Type 4 - Source Quench - the source is sending data too fast for the receiver (Code 0), the buffer has filled up, slow down!