Hello,
Sorry for the late response. Well, you can try calling GetDistanceRepresentation() on your vtkDistanceWidget object. In C++, it returns a crude pointer to a vtkDistanceRepresentation object. In Python, I believe it returns a writable reference to an object. Then, you can call SetScale(3.28084) on it to render distances in feet (supposing your model data are in meters).
best,
PC