There's nothing like that just yet, I'm afraid, but that's a nice addition to make. I'll take a look into it.
For now, you might get some milage by watching for DOM mutation events in newer browsers (although that whole API is unstable and being replaced in DOM4, so ymmv), but our initialization code will run
replaceChild on all the embed codes with their iframe replacements, so you might be able to use it still.
As I say, we'll look into giving you a proper callback interface soon.