I'm a bit confused by your survey, you mention that you are wanting to explore stereotypes of Westerners in Japanese CMs but in the examples that you reference the celebrities in the ads aren't really being overtly stereotyped. In fact the examples you've mentioned are more examples of American celebrities being used as "name brands" in association with products that they are promoting than them being mocked or stereotyped. There's a whole website devoted to American/Western celebrities in Japan which includes other examples:
Japander.com
The celebrities used in the ads mostly play themselves or the characters that they are known primarily for (i.e. Kiefer Sutherland's "24" character). Even the Arnold Schwartzenegger ad example is more about him acting humorous/crazy for the camera than him being stereotyped as a "gaijin".
This Youtube example is more along what I think you are wanting to examine (this one looks at the reverse "orientalism"/Asian stereotypes in Western Commercials):
YouTube - Anthropology Project: Orientalism in Advertising
I tend to think there's more examples that can be found of Asian stereotypes in Western Commercials and Adverts than with "gaijin" stereotypes in Japanese CMs. I do however think that in regular Japanese TVs and Movies, there might be more examples of Westerner stereotypes.