Hi Tom,
you basically answer the question by yourself. You need to give RC enough images to slowly transition. As for the best way to do that, everybody has to figure that out for themselves - it depends on so many things. Shadows from a flash is certainly a possibility and switching it on and off as needed probably the best way to handle it.
What I realized only not too long ago is that RC can work best with surfaces that are close to parallel to the sensor plane (pointing the camera orthogonally at them), hugely angled surfaces ( more than 20-30°)are very difficult because the features change magnitudes more than with parallel surfaces.