As someone responsible for interviewing technical candidates, I love this.
It might be a bit of a hyperbole to suggest that a stammer is an advantage in an interview, but you could view it as an opportunity. The entire purpose of an interview is to get a sense of the skill level of the interviewee. You want to know how they respond to problems. Are they able to arrive at solutions?
Your stammer is an opportunity to show that you know how to work your way through a challenge. And don't fool yourself in to thinking that using any of the solutions suggested here diminishes the accomplishment of working through your challenge. Knowing where to seek help, then taking the appropriate action based on that advice is a skill. You'd be amazed how many people do not know how to effectively seek outside help.
If I were interviewing someone with a stammer and they handed me this card, it would put a huge smile on my face. It would shift my disposition in a positive direction, which would definitely impact the interview. How could it not?