Exceptions don't need to be made. It just plain doesn't work. I've banned and removed posts/threads from that user once on Tom's Guide and 3 times on Tom's Hardware just to make sure I hadn't missed anything, and the posts are still there. The problem is the shoddy interaction between the US and the (redundant) UK site.
The current system is an ever-expanding patchwork of partially compatible software and permissions/functionality for regular users and moderators alike aren't always consistent between them. There's a new software platform being built at the moment which will hopefully put this lack of uniformity to death.
Even if it added an extra step, I wouldn't mind a challenge/response system intended to block automated postings.
Or, obtain as much information as possible on the offender and post it somewhere public so any interested party can investigate further if necessary and/or terminate the offender.
Oh the joys of a system that was sort of macgyvered but mostly just slammed together, i work with a Frankensteined system daily i understand your pain, its probably going to take someone on the BoM staff with DB access to fix some of the issues.
Adding a captcha for new users would at least slow the spam down, maybe until you hit 100 posts there is a captcha before you can post a comment, would at least slow them down so their account can be nuked before they spam everything.