[Baalz]

Here's the fix for the scenario you describe (assuming the players are there for a friendly game) - just have the two skilled players start the game at war with each other and can never agree to peace or work together. Wouldn't work all the time, but the specific game you mention has just the right balance that this should work fairly well, even if the 2 skilled players are not equally skilled. It'd probably play out with the skilled players trying to court the less skilled (and likely smaller) players to help them out rather than their opponent, while anybody being gobbled up by one of the skilled players could expect direct and indirect help from the other one (including strategy advice).