I am not sure about the extension rod, but my understanding is that you CAN control the sensitivity of the gimbal settings of Mini Control Stick if used with a Pocket 2. So perhaps it will work with the Extension Rod? I have confirmed however that these gimbal settings are not available for the Mini Control Stick when used on a Pocket-1.
Frankly, I think that DJI's claim that the Mini Control Stick is 'backward compatible with the Pocket 1' is false advertising. Yes, the pan left / right / up / down works, and the button to set Follow / Tilt Lock / FPV modes work, but the ZOOM feature and the Gimbal Settings options are NOT supported on the Pocket 1.