Ian, I just wanted to say that you might not need to implement a corresponding transmit mode. It's easy enough to translate between the original IR Toy bit format and a sequence of durations.
Of course, if something like WinLIRC would work better with such a mode, and it cannot be implemented easily in the WinLIRC driver, then it's certainly worth the effort to add a transmit mode. But unless it's crucial, I'd say that you should feel free to focus your efforts on other tasks.
(this comment is based on your recent blog entry)
Since the framework is already there from the IRIO mode code, it won't be to bad to implement.