Your eyes shouldn't be diverging, just not converging (it's often called "parallel" viewing). It is more difficult to learn, and the offset between the images is more sensitive (since, as you say, actually diverging your eyes is near impossible).

However, when you've mastered it, and when the offset (i.e. size) is correct, it's much easier to snap into than the cross-eyed viewing, and much easier to stay in focus while looking at different parts of the image.