Feature Request: Perform block synchronously

[zakdances]

I'd REALLY like an easy, convenient way to choose to perform any of the BlocksKit methods in a synchronous/blocking and (optionally) main-threaded manner. There are times when I want the functionality of BlocksKit but I need it done on the main thread (like a normal non-block method) to stay in sync with the rest of my app. Also it would be great if BlocksKit could extend this feature to all blocks. This feature would be tremendous!