Change your goals... Go for communism and then espionage... Vet Spies are the great equalizer.
And while in communism, use it. Go to war.
Swamp him with units. Yeah, all three of you can go for his throat, but realistically, two people on different fronts can drive him nuts. If he beats you to nukes, and you don't have SDI's yet, it is probably over... But make sure you have a city of his that hasn't had a science stolen by a diplo. A vet spy can steal repeatedly from a single city as long as a diplo didn't raise the steal flag. You can make life miserable for him.
Good Luck!