First off, the wedding is on July 4th, a national holiday filled with fireworks... Maybe your friend is into big loud explosions and crazy things like this. So he could be making this up to cause some "fireworks" in his own life...
Second, he's dating a girl that is hot but not too smart. He obviously chose her so he could get away with his fiery, manipulative, lying ways. He could fool her into getting pregnant without realizing he did it.
Third, he's obviously lying about the just kissing part. Something happened. How he kept the girl from knowing it was happening is a mystery to me, but with her being so dumb, he somehow found a way.
Fourth, this is obviously a cleverly manipulated ploy to make sure he doesn't have to pay child support once they inevitably divorce. I guess you have to give him credit for planning ahead of time.
How should you handle this? Go back to point one. Thrill your friend with fireworks. I recommend bottle rockets because they can be aimed quite well and have deadly accuracy. Make sure you get him in an open field when he is not expecting it. Then shoot off fireworks and give him the kind of show he wants!