Filtering events categories by date

It's easy to return events within a certain date range, but it would be handy to be able to return event categories in use within a date range.

On the John Smith's website, I used the Events app for the race dates section. I set up race courses as event categories and race dates as events. In order to plot participating race courses in the current calendar year, I returned the array of all events for the current year, and built a de-duped array of categories used.

It helped that for obvious reasons, an event could only happen in one place :)

While it was possible to work around this limitation, it would be nice to be able to have a perch_blog_categories_custom function or something along those lines...