I cannot give you any source, unless you want to waste hours of your time watching some car videos. The difference between an n-word pass and rice-pass is what you mean with that. Some secret way of saying the n-word does not change its racist connotation but a ricer by default has nothing to do with race. If you want to be racist, you would have to explicitly specify that you are talking about the owner's race or the car's origin or whatever.

The term is so far removed from any malicious origin, that some people wouldn’t even know they should feel offended, unless someone told them they should be.

That's not normal human behavior. Try to imagine it. 3 people are going down the street. One of them points out that a car on the street is "riced". Second one tells the third who is of Japanese origin, that he should get offended because of the word's origin. It would be weird to get offended because someone told you to.