Sorry - this never really became important enough for enough sites (well, paying clients!) for us to implement it.
Voice development and hosting is funded by clients who pay to use the platform - such as Surrey Community. So development tends to be focussed only on those areas that our clients feel are most beneficial to their users.
So, for the foreseeable future, I'm afraid you're stuck with manually creating the events for the last Thursday of each month.
Joe - Voice Admin