I took the even easier (albeit, more time consuming route). I turned on team switching, then had the comps target each others silos, airbases, and naval groups. by the time I openly backstabed, it was to late for them to fight back. Bwaahahaha!
Edit: The world gone mad! Two of these CPU's managed to end up with -0.0m survivors. And that's with out going over the 200m limit population. Must be a bug in the new 1.4 two Beta....