http://www.sendspace.com/file/u1wcw5
Using five computer keys or midi controllers, you can control the Loop Record Start/Erase, Overdub, and choose between 1,2,4 and 8 bars.
Everything is setup as needed, just map your computer keys or midi controller like the following picture.

If you added some dummy clips to quantize things, you could probably get even close to what you're looking for. I'm too tired to work on it more right now.
This definitely has room to be improved on, I'm sure it can be cleaned up a bit, plus the way it is midi-controlled can be changed for personal preference. Not to mention filters and such.
If anyone wants to improve on it, feel free!
(Also, I'm still on Live 6, on Leopard, so not 100% sure this will work the same in Live 5 or Live 7.)