Howdy nwatson,
That is actually one of our most popular feature suggestions! As you will note in that link, we are working towards adding that functionality in a future version. In fact we began work on it a while ago, but it takes a surprsing amount of changes to get that going, so you have not seen the fruits of this labor yet.
For now you must split the event in two. Soon though, it will work just like you want. Basically you will be able to add a recurrence of an event to any arbitrary date that you want to!
Does that make sense? Will that work for you? Please let me know. Cheers!
– Brook