You can get really creative with miserable users it's redirect function. Shock sites have a purpose.
Also it might be a nice idea to code this into miserable users.
I assume you have AE detector? And Paul's show real IP hack? If not then get it.
You do not have to moderate new members, but you do need to review them. One by one. There is a hack that shows the newest members on the forum index. That will allow you and your mods to review all of them and ban them on sight.
Another idea is to block all proxies. Since your troll needs to be using proxies to circumvent your IP bans, taking away proxies is the way to go. An alternative to blocking all proxies is to use a hack to move new registrants that use proxy to a moderated member group.
See: https://vborg.vbsupport.ru/showthread.php?t=131852 https://vborg.vbsupport.ru/showthread.php?t=157507 https://vborg.vbsupport.ru/showthread.php?t=96318 https://vborg.vbsupport.ru/showthread.php?t=147280