THC testing discriminatory against fat folks?

Has anyone ever thought of filing a discrimination lawsuit against employers who test for THC, due to the fact that it's easier for thin folks to pass? Since the amount of time THC remains in your system depends on metabolism and body fat, drug testing is inherently discriminatory against the obese. This seems unfair, and I suggest some folks get together and file a class-action lawsuit. If I weren't a virtual skeleton, I'd file it myself, but I think it would be a bit more believable if some more full-figured folks filed it.
So has this been though of millions of times before, or am I some sort of innovator? (Probably the former, of course).

^.^ Lovely idea.

Genius. Frickin' Genius.

I say go for it!