heres my idea, john smith, assistant to the chief marketing director of blandco and an avid coffee enthusiast. while normal looking he has quirky quotes like "the blend", "are you feeling it?", or "let the mundanity flow through you". getting enough relationship levels allows non-cosplayers to tip depending on novelty. if you really want to there can be a twist where in fact he is a person cosplaying as a office worker character from a realistic fiction series. he is just suuuper in character about it.
he would of course hold a cup of coffee and take occasional sips from it, and if you wanna be real fancy you can have him hold whatever is on the menu at the time.