Can you take them for a drink after work one evening and tell her/him how much you like them and how you wouldn't dream of saying the this in front of anyone at the office so thought this would be a great idea !

Tell them that you get headaches when you have to speak too often that you have always been like this and so need some peace throughout the day.

Is it possible for you to tone down the speaking a little for you ?

Say it with a smile. And plenty of assurance that you like her/him.

Its not lying as it is getting to you.