Daniel Lima shares a tool that he has been working on for more than a year, in his spare time. Sculpt Inbetween Manager will allow you to bake pose space deformation, mirror targets, and edit their deltas, essentially administrating in-between poses and their attributes.
Sculpt Inbetween Manager allows the artist to sculpt inbetweens on pose and manage their attributes
Daniel was inspired by features in other applications such as Softimage, and sought to bring similar controls to Maya with Sculpt Inbetween Manager. The Pose Space Deformation will allow you to actually sculpt on a pose, based on implementations created from papers by J.P. Lewis, Matt Cordner and Nickson Fong.
Check out the Sculpt Inbetween Manager Python Script for Maya here.