Do not worry at about treating a client with Bell's Palsy. The cause for this condition is a virus that attacks the 7th nerve and that nerve controls the entire side of the face and its facial muscle function. What you do want to do is show empathy and compassion for this person. I cannot go into detail but I assure you that this person is going through a very difficult time.
What you will need to look at his BLINK reflex and the ability to control the corner of the mouth. The reason is that yoiu obviously do not want anything to enter where it should not. Keep an eye on that and you should be fine.