First off, props on being a great person! Very nice of you to try and figure out how to make him more comfortable. I would start off by just assuring him that you don't mind and that the stutter is not a big deal to you. But if he starts stuttering, try your best to maintain eye contact. I can usually tell just through body language whenever someone gets a little uncomfortable once I start stuttering, which in turn makes me uncomfortable. Eye contact is the biggest thing here. Keep in mind that nerves/emotion don't always cause a stutter. Sometimes it just happens because it happens. Other than that, it's more of a matter of him getting more comfortable around you in-person. Chances are he's going to be nervous going on this date so he'll probably stutter more than he normally does, especially if he has some social anxiety. Also, try not to finish his sentences unless he specifically says otherwise. This is is usually a touchy place for some with a stutter. Good luck! *EDIT: Words.