This script will create a locator, named based on the selected mesh, populated with Attributes, named off of the blend shapes connected to the mesh and then set driven keys so that each Blend shape is keyed to an appropriately named attribute on the locator to be off at 0 and fully activated at 100.
The tool supports the use of both In-Between targets and Combination Targets.
Given a character with a blend shape based facial rig, rather than set your driven keys one by one, you can simply select the head and run the script which will set-driven-keys to attributes, named after their source target, on a locator in just a few seconds.
How to use it:
Select the mesh you want to map blend shapes for.
Run the script.
Open the .py file in any text or script editor.
Paste the entire contents of the .py file into the Maya Script Editor.