Why would you not just start manually verifying members at this point?
Congrats SimonAllen, accepted exactly 5 months ago today; before that, the rate was once per month, and it has only gotten worse since Phillip said he would address it which was an anomaly within itself.
This is done to filter out spambots? You might as well just let everyone in at this point and actually start managing the forum. Add a staff member or two... fuzzygobo for instance seems more than capable of the task if he wants to. Other than that, an obvious candidate is D'Snowth.