Make Shotwell list events by year instead of by month

While re-discovering Shotwell after upgrading to Ubuntu 13.04, I started organizing my photo album for real. I quickly noted that I prefer a quite wide classification of events, so that one event usually spans many days (sometimes even weeks - a vacation trip, for example). Shotwell handles this very nicely by displaying the first and last dates of photos in the event - but it still sorts the events by month in the side bar:

Since these events often span over month boundaries (even if it's just August 29 to September 3) I'd rather just have all the events sorted by year. However, I can't find any settings related to this. Is there a way to change this view?

Note: I don't care about folder structure on the file system here - that I have setup just as I want it. This is just the event browser inside Shotwell.