This tool is part of my personal toolset.
It let's you easily create, connect and animate animation based corrective blendshapes,.
Just go to the frame you want to correct/deform, hit "Sculpt" and edit the shape of your mesh. The cool thing is that the script works on pose: you can sculpt the corrective shape in any pose, then the script will bring back your deformed mesh in base pose automatically to create your corrective shape.
Coded in python.
http://www.tommasosanguigni.it/blog/?p=111