None.
So, I found out about this thread http://beta.scratch.mit.edu/discuss/topic/1810/ - and I decided to try out their idea. The end result is this project. I made a custom block that has a list of the sprites as a drop down! I can only imagine what I could do with this. :P EDIT: It does seem like this loophole might be closed in the future as to prevent Scratchers from getting confused with the scripts - so I'd probably recommend against doing this. But you can knock yourself out for now.
