Suggest to setup a dedicated queue for moderators to review questions that hang in Stack Overflow CV queue for more than specified amount of time - say for 5, or 10, or 20 days, or maybe for a month.
- For this queue, suggest to have no review limits set (as moderators are expected to be trusted), allowing them to pick the comfortable rate at their discretion. Also I am not sure if audits or badges make sense there.
Taking into account absence of review limits, along with the fact that per my observations, moderator vote is binding in the sense that both Close and Leave Open drop the questions off the "main" CV queue, I would expect this to help in handling "long tail" of the CV queue.
Above assumes that moderators are interested in helping community to handle CV queue. This assumption is in turn based on my observations, for example of current top reviewer being a moderator with fairly respectable 12K+ reviews. Also, I noticed that several dozens of my flags bringing mod attention to particularly tricky cases in CV queue at Programmers were actioned with an impressive consistence (in comparison, other kinds of my flags result in no action from time to time).
For a somewhat similar suggestion, take a look at Let moderators navigate the review queues at will - mine is different in that suggested queue is designed to pick and serially present particular kind of troublesome items for mod attention.