I would also add that you might try to practice with a bit of soap on your face, and a plastic knife - like from a fast food place. Shave all the soap off with opposing hands.

I think the TOUGHEST thing with shaving with the non-dominant hand is getting the ANGLE of the blade to face correct! Once that is accomplished, it moves pretty fast from there.

Learning to shave with the non-dominant hand is an invaluable skill in straight razor shaving....