Just a thought... before talking about "forcing" folks to attend, *asking* them first might be most appropriate.

But as the largest economy in the world, it's quite simple. Attend, or we don't sell you anything, give you any military aid, or buy anything from you. Period.

Would suck if the Sauds didn't show up though...

But there's asking and there's asking. Deputizing significant and well-respected allies (like the King of Jordan) to approach countries with which they have good relations would be more diplomatic.