That would mean they're non rich media, no? If so, I'd say they most likely have much LOWER engagement levels - rich media usually beats the pants off flat banners in head-to-head tests.
Can you make custom right-click menus for Flash objects?
Its kind of a moot point really - the industry standard action script opens a new window. Any website that redirects away from its content to look at an advertisers page is a little misguided.
I am moderating all comments to weed out spam (there's a lot of it). Comments are usually approved within a day.