As has been mentioned, whatever you do DO NOT run at him with your hands extended.
It will be curtains for you pal. Ive had the oppurtunity to train with a highly ranked Aikido expert and to be honest I wasnt that impressed. He had an inflated opinion of what he could with his abilitys and upon demonstration in a "what if they do this" scenario for the class had no answer for my MT clinch which would have opened his eyes had I choosen to spin him and actually deliver knees. As it stood, I didnt want to embarass the man in front of 30 students.
Combat Aikido may be a completely different story, but I wouldnt let this "lull" you into believing its going to be a cake walk. He may very well be extremely well rounded, but its a safe bet the skills you will face from a true Aikido practitional well involve techniques from close quarters, they usually like to work off being grabbed or chased in a manner like you're trying to grab them. You should expect some type of throwing abilitys, depending on how advanced the guy is.