How to rig a driver for a Corrective Shape on Rigify?

Hi,
I’m having the follow problem:
I made a corrective shape for the thigh. It suppose to work with a rotation transform driver, but the thigh bone never rotates because it’s constrained!
The driver suppose to get the DEF-thigh.L.01 rotation to apply the shape. Applying on this bone I wouldn’t worry about IK or FK leg animation. Or there is a better solution?

So, how can I make this work?

Cheers

deformExample.blend (412 KB)

You could use rotational difference between the DEF-thing.L.01 and say, the root, or pelvic bone. Here’s an immensely contrived, hackish example.

Hope that helps.