hey that's a very nice idea!
too bad I have a long to-do list and cant code this hack, I would love to. If someone takes it on, may I also suggest there may be a part to design and submit a new postbits to site and after admin approval, they will be added to the database for future selection. Just like a "custom postbit editor" for advanced users.. And dont forget to add a "preview" part in the selection screen.