1 pointguys, please PM me links to those incompatible modules, I'll check them and let you know. I'm quite curious what the problems are.
1 pointModify your themes maintenance.tpl file. Beyond that I'm sure there must be modules out there that would do it.
1 pointyou can replace $this->errors = Tools::displayError('Invalid Content'); with die(Tools::displayError('Invalid Content')); The result will be ugly white page, but that's ok, since this should be visible to attackers only